linux.sgml

<qandaset defaultlabel='qanda' id='linux'>

<title>Linux Frequently Asked Questions</title>

<qandaentry>
<question>
<para>
What version of Linux am I running?
</para>
</question>
<answer>
<para>
<orderedlist>
<listitem>
<para>
Use data from the 
<ulink url="http://www.linuxbase.org/"><citetitle>Linux Standards Base</citetitle></ulink>, on
<ulink url="http://www.debian.org/"><citetitle>Debian</citetitle></ulink> it can be read from
<filename>/etc/lsb-release</filename>.
</para>
</listitem>
<listitem>
<para>
To get your system information, use
<programlisting><![CDATA[
uname -a
]]></programlisting>
</para>
</listitem>
<listitem>
<para>
To show release information (Debian, Ubuntu), use
<programlisting><![CDATA[
cat /etc/lsb-release
]]></programlisting>
</para>
</listitem>
</orderedlist>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to create a picture summary of images in a directory?
</para>
</question>
<answer>
<para>
This command will generate a postcard size summary of images
<programlisting><![CDATA[
convert 'vid:*.jpg' directory.miff
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to resize directory for preview with the GIMP?
</para>
</question>
<answer>
<para>
<programlisting><![CDATA[
for f in *.jpg; do convert -size 80x60 $f ${f#../};done
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to rotate a picture right by 90 degrees?
</para>
</question>
<answer>
<para>
<programlisting><![CDATA[
mogrify -rotate 90 p6260018.jpg
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to total directory sizes?
</para>
</question>
<answer>
<para>
<programlisting><![CDATA[
du -sch [directory] ...
]]></programlisting>
</para>
<para>
<example>
<title>To summarise size of a list of directories</title>
<screen>
$ du -sch pictures/ music/ documents/ 
8.0G    pictures/
698M    music/
1.2G    documents/
9.9G    total
</screen>
</example>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to clear or empty log files?
</para>
</question>
<answer>
<para>
To maintain a log directory
<programlisting><![CDATA[
cp file.log file.log.0
cat /dev/null > file.log
compress file.log.0
]]></programlisting>
</para>
<para>
General rule of thumb
</para>
<para>
Do not remove log files - null them. If you just remove the log file and a
process has the file open, this space will not be reallocated until the demon
is stopped.
</para>
<para>
To empty a log file
<programlisting><![CDATA[
cat /dev/null > file.log
find /tmp -name '*.log' -exec cp /dev/null {} \;
echo > file.log
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to label tapes?
</para>
</question>
<answer>
<para>
You can label tapes by
<programlisting><![CDATA[
mt -f <tape device> rew
echo "tape label and date etc"|dd of=<tape device>
dump filesystems
mt -f <tape device> rewoffl.
]]></programlisting>
</para>
<para>
When you want to retrieve the tape label do
<programlisting><![CDATA[
dd if=<tape device>
]]></programlisting>
</para>
<para>
When retrieving filesystems, just remember to skip the first save set as it
is the label.
To retrieve the 2nd filesystem dumped do
<programlisting><![CDATA[
mt -f <tape device> rew
mt -f <no rewind tape device> fsf 2
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to forward email?
</para>
</question>
<answer>
<para>
Add the following entry to <filename>$HOME/.forward</filename>
<screen>
\frank@localhost, frankhjung@linux.com
</screen>
This says that mail should keep one copy for the local account, and send one
copy to my internet account.
</para>
<para>
When on vacation, do this
<screen>
\frank, "| /usr/bin/vacation -r 0 frank"
</screen>
This keeps one copy for the local account, and sends a vacation message stored
in a file called <filename>$HOME/.vacation.msg</filename> back to the sender of any
mail.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
What mail is currently queued to send?
</para>
</question>
<answer>
<para>
If you are using <command>sendmail(8)</command>, then
<screen>
sendmail -bp   
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
What does the ? mark mean under the tty field in the process status (<command>ps -ef</command>)?
</para>
</question>
<answer>
<para>
The "?" mark indicates that the process is not attached to any terminal.
This happens typically for daemons, where the process becomes the leader of the
group and detaches itself from the terminal.
</para>
<para>
See also <command>pstree(1)</command> and <command>ps axf</command>.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to show which users have not logged on recently?
</para>
</question>
<answer>
<para>
The following script reports users who have recently signed in/out.
Limitations: doesn't register remote logins.
<programlisting><![CDATA[
#!/bin/ksh
# Display Recent Logins
# This is really slow for large "last" - so simplify
last | cut -d" " -f1 | sort -u > ./last.out
for i in $( cut -d: -f1 /etc/passwd | sort -u )
do
   grep $i ./last.out > /dev/null
   if [ $? -eq 0 ]
     then print $i"\tOk"
     else print $i"\tNone"
   fi
done
rm ./last.out
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to format an ASCII file into PostScript?
</para>
</question>
<answer>
<para>
This example uses <command>a2ps(1)</command>. Print PostScript to an ASCII
printer by piping to <command>ghostview(1)</command>
<programlisting><![CDATA[
lp filename | a2ps -2q --strip=3 -o -|gs - -sDEVICE=ljet3 -sOutputFile=|lpr
]]></programlisting>
Alternatively
<programlisting><![CDATA[
gv filename | a2ps -P display
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How can I collect all input and output in a terminal session?
</para>
</question>
<answer>
<para>
Try <command>script(1)</command>, for example
<programlisting><![CDATA[
script -a filename            // this appends to filename
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to send a binary files when using email?
</para>
</question>
<answer>
<para>
Compress with uuencoding
<screen>
tar cf - files | gzip | uuencode files.tar.gz &gt; files.tar.gz.uu
</screen>
To extract use
<screen>
uudecode -p files.tar.gz.uu | gzip -c -d - | tar xf -
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to generate random numbers from a shell?
</para>
</question>
<answer>
<para>
To generate a random number, using Korn Shell, between $LO and $HI
(inclusive), use the following code
<programlisting><![CDATA[
#/bin/ksh
(( RANGE = HI - LO + 1 ))
(( NUMBER = RANDOM % RANGE + LO ))
# $NUMBER now contains your "random" number in the specified range.
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to remove a directory that is too deep for <command>ls(1)</command> or
<command>rm -R</command>?
</para>
</question>
<answer>
<para>
Use following script (which does not use <command>pwd(1)</command>)
<programlisting><![CDATA[
#!/usr/local/bin/bash

# Recursive Traversal of Directories
rm_branch () {
   # go to bottom of directory tree
   if [[ -d $dirName ]]; then
      print "going into directory $dirName"
      cd $dirName; 
      rm_branch
   else
      print "at bottom of $dirName"
      return 0
   fi

   cd ..
   rmdir $dirName;
}

# test it
if [[ -d $dirName ]]; then
   dirName = ${1};
   rm_branch;
fi
]]></programlisting>
</para>
<para>
This is easier to implement, but very slow to execute
<programlisting><![CDATA[
#!/bin/local/bin/bash

rm_branch() {
   if [[ -d $dirName ]]; then
      DIR=$dirName
      while [ -d $dirName ]
      do
         mv $dirName $dirName.x
         cd $dirName.x
         mv $dirName ../$dirName
         cd ..
         rm -r $dirName.x
      done
   fi
}
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
What devices are available?
</para>
</question>
<answer>
<para>
Use the <command>lspci(8)</command>
<screen>
lspci -v
</screen>
This will provide a list of devices on this machine. See also
<command>lsusb(8)</command> for a list of USB devices, or
<command>fdisk(8)</command>. Note that devices can be mounted by device, UUID
or label. To list mounted devices by UUID use blkid(8).  Each will be mapped to
an entries under <filename>/dev/disk/</filename>.
</para>
<para>
To list block devices use <command>blkid(8)</command>.  This will also show the
associated UUID.
</para>
<para>
Another tool is <command>devkit-disks(1)</command>.  This has a dump option
that will list very detailed information of mounted devices. For example
<screen>
devkit-disks --dump
</screen>
Information about a singe device can also be captured, but for that you
need the name of the device file.  Use a combination of commands, like
<screen>
devkit-disks --enumerate 
devkit-disks --enumerate-device-files
devkit-disks --show-info /dev/disk/by-uuid/10807b5e-24f6-4031-bdd1-bd07c08afaa3
</screen>
</para>
<para>
To list input devices use <command>xinput(1)</command>.  It is a utility that
also allows you to configure and test X input devices.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
   <para>
   How to copy an audio CD (and convert to MP3 or OGG)?
   </para>
</question>
<answer>
<orderedlist>
<listitem>
   <para>
   This can be done using <command>dagrab(1)</command>, to dump an audio CD to
   disk and <command>lame(1)</command> to convert WAV to MP3.
   </para>
   <para>
   FreeBSD: To copy an entire audio CD to disk as WAV files
   <screen>dagrab -a -d /dev/acd0c -f "Sacred_Fire-%02d.wav"</screen>
   Linux: To copy an entire audio CD to disk as WAV files
   <screen>cdda2wav -x -B -D 0,0,0</screen>
   Or the more friendly
   <screen>nice cdda2wav -D 0,1,0 -alltracks -x -Q -H -S 48 -v disable &amp;</screen>
   You may also try the <command>cdparanoia(1)</command> with
   <screen>cdparanoia -w -B -d /dev/dvd </screen>
   or more simply
   <screen>cdparanoia -w -B </screen>
   The advantage of <command>cdparanoia(1)</command> is better quality and easier
   access to specific tracks.
   </para>
</listitem>
<listitem>
   <para>
   FreeBSD: To copy only certain tracks of an audio CD to disk as WAV files
   <screen>dagrab -d /dev/acd0c -f "%02d-Sacred_File.wav" 1 2 3 5 7 11</screen>
   </para>
   <para>
   Where the options to <command>dagrab(1)</command> are
   <simplelist type='horiz' columns='2'>
      <member>-a</member> 
      <member>Dumps all tracks and ignores the optional track list.</member>
      <member>-d</member> 
      <member>Sets  the  cdrom  device  name.</member> 
      <member>-f</member> 
      <member>Sets the output name for dumping tracks.</member> 
      <member>-i</member> 
      <member>Prints out the track list from the current cd.</member> 
   </simplelist>
   This will copy the Audio CD's to disk as WAV files.
   </para>
</listitem>
<listitem>
   <para>
   FreeBSD: Don't write these WAV files straight to disk though,
   as you will get a nasty audible "click" recorded between each track.
   To eliminate this click use <command>sox(1)</command> to convert to raw
   audio
   <screen>for f in *.wav; do sox $f ${f%%wav}raw; done</screen>
   </para>
</listitem>
<listitem>
   <para>
   Linux: You can seperate these file into volumes with
   <screen>v=01 &amp;&amp; for f in audio_??.wav; do mv $f audio_${v}_${f##audio_}; done</screen>
   </para>
</listitem>
<listitem>
   <para>
   To convert WAV to OGG Vorbis format use
   <command>oggenc(1)</command>
   <screen>oggenc *.wav</screen>
   </para>
</listitem>
<listitem>
   <para>
   To convert WAV to MP3 use
   <command>lame(1)</command>
   <screen>for w in *.wav; do lame -h $w ${w%%wav}mp3; done</screen>
   </para>
</listitem>
<listitem>
   <para>
   To convert MP3 to OGG use
   <command>mp32ogg(1)</command>
   <screen>mp32ogg  --preserve-timestamp [dir1] [dir2] ...</screen>
   </para>
</listitem>
<listitem>
   <para>
   To convert OGG to MP3 use
   <command>soundconvert.pl(1)</command>
   <screen>for f in *.ogg; do soundconvert -o MP3 "$f"; done</screen>
   </para>
</listitem>
<listitem>
   <para>
   To determine space used by mp3 files use
   <screen>du -mc *.mp3</screen>
   Or by album
   <screen>for ((i=1;i&lt;10;i++)); do du -cm audio_0${i}_??.mp3; done</screen>
   </para>
</listitem>
<listitem>
   <para>
   FreeBSD: To write to CD use <command>burncd(1)</command>:
   <screen>burncd -s 8 -f /dev/acd0c audio *.raw fixate</screen>
   </para>
   <para>
   Linux: To write to CD use <command>cdrecord(1)</command>:
   <screen>cdrecord -v -ignsize speed=6 dev=/dev/cdrom -dao -useinfo *.wav</screen>
   or, which uses TAO single session write mode:
   <screen>cdrecord -v speed=8 dev=0,0 *.wav</screen>
   </para>
</listitem>
<listitem>
   <para>
   Finally, if you wish to update an MP3 files ID3 tag, use <command>mid3v2</command>,
   <screen>for f in *.mp3; do mid3v2 -t ${f%%.mp3} -A "The Pod Delusion" $f ; done</screen>
   This sets the title and Album.
   </para>
</listitem>
</orderedlist>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to copy  data CD?
</para>
</question>
<answer>
<para>
<orderedlist>
<listitem>
    <para>
    Copy a data CD
    <screen>
    dd if=/dev/cdrom of=image.iso
    </screen>
    This command can also be used to write an ISO image to a USB device
    <screen>
    dd if=/path/to/iso of=/dev/usb_device
    </screen>
    </para>
</listitem>
<listitem>
    <para>
    Check image before writing
    <screen>
    mount -t iso9660 -o loop image.iso /mnt/cdrom
    </screen>
    This uses the loop back device.  See <command>mount(8)</command> and search
    for a section entitled "THE LOOP DEVICE".
    </para>
</listitem>
<listitem>
    <para>
    Write the image to the CD
    <screen>
    cdrecord -v -speed=6 dev=/dev/cdrom image.iso
    </screen>
    </para>
</listitem>
</orderedlist>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to record a multi-session CD?
</para>
</question>
<answer>
<para>
This answer is for use of <command>cdrecord(1)</command>.
Recall for a single (or first) session CD, follow this plan
<orderedlist>
<listitem>
    <para>
    Find location of CDRW device.  This will be used in dev option of <command>cdrecord(1)</command>)
    <screen>
    cdrecord -scanbus
    </screen>
    </para>
</listitem>
<listitem>
    <para>
    Write ISO image
    <screen>
    mkisofs -R -J -o image.iso /thedirectory/
    </screen>
    </para>
    </listitem>
    <listitem>
    <para>
    Write the image to the CD
    <screen>
    cdrecord -v -speed=6 dev=/dev/cdrom image.iso
    </screen>
    </para>
</listitem>
</orderedlist>
Now, for a multi-session CD use
<orderedlist>
<listitem>
    <para>
    Where did last session finish?
    <screen>
    info=`cdrecord -msinfo dev=/dev/cdrom`
    </screen>
    </para>
</listitem>
<listitem>
    <para>
    Use the previous session information to build new ISO image
    <screen>
    mkisofs -C $info -o image.iso /thedirectory
    </screen>
    </para>
</listitem>
<listitem>
    <para>
    Add -multi option when writing multi-session disks
    <screen>
    cdrecord -v -multi -speed=6 dev=/dev/cdrom image.iso
    </screen>
    </para>
</listitem>
</orderedlist>
</para>
<para>
To test an ISO image before writing, use
<screen>
    mount -t iso9660 -o loop image.raw /mnt/image
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to blank a re-writable CD?
</para>
</question>
<answer>
<para>
This answer is for use of <command>cdrecord(1)</command>.
</para>
<para>
To blank a CDRW use
<screen>
    cdrecord -v dev=/dev/cdrom blank=fast
</screen>
Other options for blank are all and session. This uses <command>wodim(1)</command> under the covers.
<screen>
    wodim blank=fast dev=/dev/cdrom
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to manage a CUPS printer?
</para>
</question>
<answer>
<para>
<orderedlist>
<listitem>
    <para>
    CUPS has a web management interface here 
    <ulink url="http://localhost:631/admin">http://localhost:631/admin</ulink>.
    </para>
</listitem>
<listitem>
    <para>
    As superuser start CUPS printer daemon with
    <screen>
    /etc/init.d/cupsys start
    </screen>
    Cups configuration is in <filename>/etc/cups/cupsd.conf</filename>.
    </para>
</listitem>
<listitem>
    <para>
    To see printer status use
    <screen>
    lpstat -t
    </screen>
    </para>
</listitem>
<listitem>
    <para>
    To remove all spooled job entries use
    <screen>
    lprm -P OfficeJet -
    </screen>
    </para>
</listitem>
</orderedlist>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
Is it possible to grep through a directory and all subdirectory's of that
directory?
</para>
</question>
<answer>
<para>
<screen>
    $ find directory_name -print | xargs grep required_pattern
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to FTP using a script?
</para>
</question>
<answer>
<para>
Use the $HOME/.netrc resource script.  For example
<programlisting><![CDATA[
#!/bin/ksh

#
# Start of Program Timestamp
#
echo `date +'%Y-%m-%d %T Program Started'` $0

# define constants
REMOTEHOST=255.255.255.255  # your IP address here
FILE="file_name_here"

# Create .netrc file in $HOME the ftp resource script
echo "machine $REMOTEHOST
login username
password userpassword
macdef init
cd directory_name_here
binary
get $FILE
bye

" > $HOME/.netrc

# for ftp to use the .netrc from $HOME you MUST have these rights
chmod 600 $HOME/.netrc
ftp $REMOTEHOST

# Now remove .netrc
rm -f $HOME/.netrc

#
# End of Program Timestamp
#
echo `date +'%Y-%m-%d %T Program Ended'` $0
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How can you turn off cookies?
</para>
</question>
<answer>
<para>
You can forcibly switch off cookies in Communicator/Navigator by
<command>
rm -f ~/.netscape/cookies
ln -s /dev/null ~/.netscape/cookies
</command>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to add five years to a date and display in following format dd-mmm-YYYY?
</para>
</question>
<answer>
<para>
From a shell script this can be achieved by
<screen>
date "+%d-%b-$((year=$(date +%Y)+5))"
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
What is the regular expression need to match a 24 hour clock?
</para>
</question>
<answer>
<para>
Try
<screen>
([01]?[0-9]|2[0-3]):[0-5][0-9]
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
Is there a way to change the date timestamp on a file?
</para>
</question>
<answer>
<para>
Use <command>touch(1)</command>, and using the arguments (months, days, hours,
minutes, optional century and years, optional seconds) instead of the
current time
<screen>
touch -t MMDDhhmm[[CC]YY][.ss]
</screen>
If the -t option does not exist read the man page for the equivalent.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How can you extract from a corrupted TAR file?
</para>
</question>
<answer>
<para>
In many case if there is a corrupted tar file, the following command can
be used in an attempt to extract the file
<screen>
cat [tar-filename] | tar -xvf -
</screen>
Where "-" is the <filename>STDOUT</filename>.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to compare files and show differences?
</para>
<para>
I have 2 text files, (text1 and text2), which are both about 2000 lines long,
and almost identical, except for some minor differences.
How do I print lines that appear only in file text1, and not in the file text2?
How can I print the differences into a third file?
</para>
</question>
<answer>
<para>
Use <command>comm(1)</command> command.
<screen>
comm text1 text2
</screen>
This will print 3 columns
<simplelist type='horiz' columns='1'>
   <member>1st column contains lines in file text1 only</member>
   <member>2nd column contains lines in file text2 only</member>
   <member>3rd column contains lines that are in both file text1 and text2</member>
</simplelist>
You can then mask any of these columns by
<screen>
comm -23 text1 text2
</screen>
This will not print column2 and column3, giving you lines available in
text1 and not in text2.  This output can then be redirected to a file.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How do you do decimal calculations in a Shell script?
</para>
</question>
<answer>
<para>
Use <command>bc(1)</command>
<example>
<title>To calculate 12/3</title>
<screen>
echo 12/3 | bc -l
4.00000000000000000000
</screen>
</example>
So to do this in a script do something like
<programlisting><![CDATA[
#!/bin/ksh
# Decimal Calculations
if [[ $# -eq 3 ]]; then
   echo "$1$2$3" | bc -l
fi
]]></programlisting>
</para>
<para>
As an aside, <command>bc(1)</command> can also be scripted to perform calculations.  
<example>
<title>Count from 1 to 10</title>
<programlisting><![CDATA[
#!/usr/bin/bc -q
for ( i=0; i<10; i++) {
   print (i+1) % 12, "\n"
}
quit
]]></programlisting>
</example>
Which is just a complicated way to count from 1 to 10.
</para>
<para>
In <command>bash(1)</command> you can count from 1 to 10 by
<programlisting><![CDATA[
for ((i=1;i<11;i++));
do 
   echo $i; 
   read; 
done
]]></programlisting>
</para>
<para>
You can take it one step further by using <command>expr(1)</command>
<programlisting><![CDATA[
for ((i=4;i<9;i++));
do 
    echo mv ring4-$i.jpg ring4-0`expr $i - 3`.jpg;
done
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to synchronise system date?
</para>
</question>
<answer>
<para>
Using <command>ntpd(8)</command>
<screen>
server 0.au.pool.ntp.org
server 1.au.pool.ntp.org
server 2.au.pool.ntp.org
server 3.au.pool.ntp.org
server 4.au.pool.ntp.org
</screen>
To set current time, use <command>date(1)</command>
<screen>
date -s 'Sun Sep 11 21:39:58 EST 2011'
</screen>
Then set hardware clock using <command>hwclock(8)</command> from current system clock
<screen>
hwclock -w
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to add new fonts to X11?
</para>
</question>
<answer>
<para>
Please add all new fonts to new sub-directories of
<filename class='directory'>/usr/X11R6/lib/X11/fonts</filename>.
</para>
<para>
   <orderedlist>
   <listitem>
      <para>untar font to fonts directory</para>
   </listitem>
   <listitem>
      <para>add new font to list in <filename>/etc/XF86Config</filename></para>
   </listitem>
   <listitem>
      <para>(re)start X</para>
   </listitem>
   </orderedlist>
</para>
<para>
New fonts can be tested by
   <orderedlist>
   <listitem>
      <para>untar font to fonts directory</para>
   </listitem>
   <listitem>
      <para>call
      <screen>
        $ xset fp+ /usr/X11R6/lib/X11/fonts/newFont
        $ xset fp rehash
        $ xfontsel
      </screen>
      </para>
   </listitem>
   </orderedlist>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
Why can't I download mail?
</para>
<para>
More precisely, why do I get this error message when running <command>fetchmail</command>?
<screen>
fetchmail: SMTP error: 451 4.1.8 &lt;name@domain.com&gt;... Domain of sender
address name@domain.com does not resolve
</screen>
</para>
</question>
<answer>
<para>
A simple explanation
<literallayout>
Posted by Adriaan Tijsseling on April 26, 2002 at 23:48:46:

If you use dialup networking and you have sendmail starting up at
boottime, then you will have fetchmail problems when trying to retrieve
mail from an external server.

Sendmail loads it's data when it starts up, but does not update with a
SIGHUP. So, if you dialup, make sure to HUP the sendmail, otherwise your
fetchmail will complain with an SMTP error: 451 4.1.8 ... Domain of sender
address foo@foo.com does not resolve. 
</literallayout>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How do you configure a modem?
</para>
</question>
<answer>
<para>
<orderedlist>
<listitem>
<para>
ppp: This is a user process PPP software package.  Normally, PPP is
implemented as a part of the kernel (e.g., as managed by
<command>pppd(8)</command>) and it's thus somewhat hard to debug and/or
modify its behaviour.  However, in this implementation PPP is done as a
done as a user process with the help of the tunnel device driver (tun).
</para>
</listitem>
<listitem>
<para>
<command>netstat</command> The <command>netstat -rnf inet</command>
command allows you to view your IPV4 routing table; tun0 is the tunnel
device driver your modem uses with PPP. Flags of UG indicate that you
have a gateway that is up. The IP address associated with this entry is
the address of your default gateway.
</para> 
</listitem>
<listitem>
<para> 
Modem Access Control
<screen>
vi /etc/group
</screen>
Change the network line to 
<screen>
network:*:69:username1,username2, 
</screen>
Where username1,username2 is a comma-separated list of the users you
wish to give ppp access to.
<screen>
vi /etc/ppp/ppp.conf
</screen>
At the end of the default section, add the following line
<screen>
allow users username1 username2
</screen>
Again, substitute the actual usernames and save the file. Now your
users should be able to connect to the Internet using ppp.
</para> 
</listitem>
</orderedlist>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to install files? 
</para>
</question>
<answer>
<para>
Use <command>install(1)</command>.
<example>
<title>Using the install command</title>
<orderedlist>
<listitem>
<para>Copy rather than move the file to install location
<screen>
install -c /home/frank/bin/save2cd /usr/local/sbin/save2cd
</screen>
</para> 
</listitem>
<listitem>
<para>To install a new file and set attributes
<screen>
install -cp -m 555 -o root -g wheel /home/frank/bin/save2cd /usr/local/sbin/
</screen>
</para> 
</listitem>
</orderedlist>
</example>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
Why do I get "bad interpreter" errors when running a script?
</para>
</question>
<answer>
<para>
If you are getting the following error
<screen>
bash: ./someScript: bad interpreter: No such file or directory
</screen>
Then, it's likely you have embedded <command>^M</command>.  So run the
<command>perl(1)</command> one liner to remove them, and all will be
happy.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
Where is xxx started during the start-up boot sequence?
</para>
</question>
<answer>
<para>
The resource configuration system reads in configuration defaults from
<filename>/etc/defaults/rc.conf</filename>, and system-specific details
from <filename>/etc/rc.conf</filename>, and then proceeds to mount the
system filesystems mentioned in <filename>/etc/fstab</filename>, start up
networking services, starts up miscellaneous system daemons, and finally
runs the startup scripts of locally installed packages.
</para>
<para>
Part of the <filename>/etc/defaults/rc.conf</filename> file
<screen>
local_startup="/usr/local/etc/rc.d /usr/X11R6/etc/rc.d" # startup script dirs.
rc_conf_files="/etc/rc.conf /etc/rc.conf.local"
</screen>
The <filename>/etc/defaults/rc.conf</filename> is a file full of useful
variables that you can set to change the default startup behavior of your
system.  You should not edit this file though.  Put any overrides into one
of the <filename>rc_conf_files</filename> instead and you will be able to
update these defaults later without spamming your local configuration
information.
</para>
<para>
The <filename>rc_conf_files</filename> files should only contain values
which override values set in this file.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How can realaudio be captured for local replay?
</para>
</question>
<answer>
<para>Take these steps to retreive a Realaudio stream and convert to WAV.
<orderedlist>
<listitem>
<para>Get realaudio from web-site using <command>vsound</command> and <command>realplay</command>
<screen>
vsound -n -f ScienceShow.au realplay http://www.abc.net.au/rn/mod/science.ram
</screen>
</para> 
</listitem>
<listitem>
<para>Convert from Sun audio to WAV
<screen>
sox ScienceShow.au MarsQuestAndBirdBrains.wav
</screen>
</para>
<para>
Get <command>vsound</command> from 
<filename class='directory'>http://www.xenoclast.org/vsound/</filename>.
</para>
</listitem>
</orderedlist>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to switch off PC Beep?
</para>
</question>
<answer>
<para>
I used both these methods:
<orderedlist>
    <listitem>
    <para>edit <filename>/etc/inputrc</filename> and 
    <programlisting><![CDATA[
    set bell-style none
    ]]></programlisting>
    </para>
    </listitem>
    <listitem>
    <para>
    use the <command>alsamixer(1)</command> or
    <command>amixer(1)</command> command to unset using
    <programlisting><![CDATA[
    amixer -c 0 set "Beep" off
    ]]></programlisting>
    </para>
    </listitem>
</orderedlist>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to format and mount a MS-DOS or VFAT device?
</para>
</question>
<answer>
<para>
It depends what type of device you are managing.
</para>
<para>
For diskette use these commands
<orderedlist>
    <listitem>
    <para>
    To format a MS-DOS diskette
    <screen>
    fdformat -f 1440 /dev/fd0
    disklabel -w -r /dev/fd0 fd1440
    newfs_msdos fd0 fd1440
    </screen>
    </para>
    </listitem>
    <listitem>
    <para>
    To mount a DOS diskette
    <screen>
    mount_msdos -u frank -g staff /dev/fd0 /mnt/floppy
    </screen>
    </para>
    </listitem>
</orderedlist>
</para>
<para>
For VFAT USB device use these commands
<orderedlist>
    <listitem>
    <para>
    To format a VFAT device (this will also set the label)
    <screen>
    mkfs.vfat -n FRANKJUNG /dev/sdb1
    </screen>
    </para>
    </listitem>
    <listitem>
    <para>
    To show label
    <screen>
    dosfslabel /dev/sdb1
    </screen>
    </para>
    </listitem>
    <listitem>
    <para>
    Mount using normal vfat entries in <filename>/etc/fstab</filename>
    <screen>
    /dev/sdb1   /media/usb   vfat   rw,user,noauto   0   0
    </screen>
    </para>
    </listitem>
</orderedlist>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
Why is the network so slow?
</para>
</question>
<answer>
<para>
One possible answer is problems resolving names.   Try commenting out
<command>bind</command> in <filename>/etc/host.conf</filename>.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to quickly compare MD5 checksums?
</para>
</question>
<answer>
<para>
To compare MD5 checksum use
<screen>
md5 -q file.tgz | diff -b file.tgz.md5 -
</screen>
Or using <command>md5sum(1)</command> 
<screen>
md5sum -c uml2-SDK-1.0.2.zip.md5sum
</screen>
Where <filename>uml2-SDK-1.0.2.zip.md5sum</filename> file contains the
checksum, followed by the file name.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to restart console mouse cursor?
</para>
</question>
<answer>
<para>
To control the console mouse (not the mouse in X) use
<screen>
/etc/init.d/gpm [start|stop]
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to reset the root password?
</para>
</question>
<answer>
<para>
Use the following option when booting
<screen>
linux init=/bin/bash rw
</screen>
This should drop you to a root shell, just edit <filename>/etc/passwd</filename>, and run 
<command>sync</command> before you reboot. 
</para>
<para>
When using the rescue disk
<screen>
rescue root=/dev/hda1 init=/bin/bash rw
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to over come a blocked site?
</para>
</question>
<answer>
<para>
If a site is blocked (such as George W. Bush's site during 2004 campaign), then
use a proxy such as Coral. ie the blocked site
<ulink url="http://www.georgewbush.com/">http://www.georgewbush.com/</ulink>
Can be viewed by Coral by appending <literal>.nyud.net:8090</literal> to give 
<ulink url="http://www.georgewbush.com.nyud.net:8090/">http://www.georgewbush.com.nyud.net:8090/</ulink>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to print special characters on console?
</para>
</question>
<answer>
<para>
Using the vim editor and you know the hex code
<screen>
ctl-v xYY = to insert character with hex code YY
</screen>
You can get the hex code of a character from vim with
<screen>
ga = character code under cursor
</screen>
To enter a special character in <command>vim</command> enter the 
decimal code. For example to print &#251;, then
<screen>
ctrl-v 251
</screen>
</para>
<para>
Special characters can be written to console (for example)
<screen>
echo $'\xFB'
</screen>
Which should print &#251;. See <command>iso_8859-1(7)</command> or
<command>ascii(7)</command> for more codes.
</para>
<para>
Alternately, a more drastic measure is <command>xmodmap(1)</command>. Under X
there are some additional tools like <command>xev(1)</command>, to print X key
events.
</para>
<para>
For XFree86, the solution is to enter xmodmap -e "keycode xx = Multi_key" or
xmodmap -e "keysym yy = Multi_key" where 'xx' is the keycode or 'yy' the keysym
of the key you choose to be the 'Compose'-key. (Use xev to get these values.)
</para>
<para>
Alternatively you can add keycode xx = Multi_key to your ~/.xmodmaprc. This way
it happens automagically.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to remove a USB device?
</para>
</question>
<answer>
<para>
You have to remove the USB module if you want to plug in another device.
To do this use
<screen>
rmmod usb-storage
</screen>
You do not need to add a USB module, since the kernel will pick this up automatically.
Before
<screen>
usb-storage            60256   0 (unused)
usb-ohci               17000   0 (unused)
usbcore                54240   1 [printer usb-storage usb-ohci]
</screen>
After
<screen>
usb-ohci               17000   0 (unused)
usbcore                54240   1 [printer usb-ohci]
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to clean-up CUPS spooled jobs?
</para>
</question>
<answer>
<para>
The following removes entries from the completed jobs log
<screen>
lprm -P OfficeJet -
</screen>
</para>
<para>
To find spooled job entries older than 7 days
<screen>
find /var/spool/cups -type f -ctime +7 -print
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
What are the files in <filename class='directory'>/var/log/ksymoops</filename>?
</para>
</question>
<answer>
<para>
These are files generated by <command>modprobe(8)</command> whenever a module 
is added or removed. There is no switch to turn logging off. The script
<command>insmod_ksymoops_clean</command> can be used to clean this directory.
Or you can delete the directory.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to capture screenshots?
</para>
</question>
<answer>
<para>
Images can be grabbed and converted to PNG format with the following commands
<screen>
xwd -frame -out temp_image
xwdtopnm temp_image  > fig1.pnm
convert fig1.pnm fig1.png
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to get reminders for important events?
</para>
</question>
<answer>
<para>
This uses the <command>calendar(1)</command> command.  It takes a simple
formatted text file as input, and displays events within a user specified
number of days forward from today.  I use this feature to remind me of
birthdays and warn me when bills are due.  It is really easy to maintain, and
versatile.
</para>
<orderedlist>
<listitem>
<para>Create a file called <filename>~/.calendar/calendar</filename>.
The file will contain tab delimetered entries like
<programlisting><![CDATA[
/* $Id: linux.sgml 900 2011-07-03 08:21:40Z frank $ */
#ifndef _calendar_frank_
#define _calendar_frank_

LANG=en_AU

#include <calendar.australia>
#include <calendar.birthday>
#include <calendar.reminder>

#endif
]]></programlisting>
</para>
<para>
And this is what a the <filename>calendar.australia</filename> file looks like
<programlisting><![CDATA[
/*
 * Australian holidays
 *
 * $FreeBSD$
 */
#ifndef _calendar_australia_
#define _calendar_australia_

LANG=UTF-8

/* Australia */
Jan 26	Australia Day Holiday (Australia, except NSW, Vic)
Mar/SunLast	Daylight Savings Time ends in ACT, NSW, SA, TAS and VIC.
Apr 25	Anzac Day (Australian and New Zealand Army Corps) Day (Australia)
Jun/MonSecond	Queen's Birthday Holiday (Australia, except WA)
Oct/SunLast	Daylight Savings Time starts in ACT, NSW, SA and VIC.

/* ACT, NSW, common */
Mar 18	Canberra Day (ACT)
8/MonFirst	Bank Holiday (ACT, NSW)
10/MonFirst	Labour Day (ACT, NSW, SA)

/* Victoria */
3/MonSecond	Labour Day (Vic)
Nov/TueFirst	Melbourne Cup (Vic)

/* Tasmania */
Feb 11	Regatta Day (Tas)
Feb 27	Launceston Cup (Tas)
Mar 11	Eight Hours Day (Tas)
Oct/SunFirst	Daylight Savings Time starts in TAS.
Oct 10	Launceston Show Day (Tas)
Oct 24	Hobart Show Day (Tas)
Nov 04	Recreation Day (N Tas)

/* South Australia */
May/MonThird	Adelaide Cup (SA)
Dec 26	Proclamation Day holiday (SA)

/* Western Australia */
3/MonFirst	Labour Day (WA)
6/MonFirst	Foundation Day (WA)
Sep 30	Queen's Birthday (WA)

/* Northern Territory */
5/MonFirst	May Day (NT)
7/FriFirst	Alice Springs Show Day (NT)
7/FriSecond	Tennant Creek Show Day (NT)
7/FriThird	Katherine Show Day (NT)
7/FriLast	Darwin Show Day (NT)
8/MonFirst	Picnic Day (NT)

/* Queensland */
5/MonFirst	Labour Day (Qld)
Aug 14	RNA Show Day (Brisbane metro)

#endif
]]></programlisting>
</para>
<para>
This is the same way I setup my <filename>calendar.reminder</filename> file.
By providing a month, day then a description I can easily maintain a reminder
system for my regular bills.
</para>
</listitem>
<listitem>
<para>
Now, activate and automatic reminder via email by adding the following entries
to <command>crontab(5)</command>.  The following will give me warning of events
7 days in advance:
</para>
<para>
<screen>
@reboot /usr/bin/calendar -A 7 | mail -e -s "Reminders from Calendar" frank@localhost
@daily  /usr/bin/calendar -A 7 | mail -e -s "Reminders from Calendar" frank@localhost
</screen>
</para>
</listitem>
</orderedlist>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
Where are the Australian mirrors for Debian?
</para>
</question>
<answer>
<para>
From
<ulink url="http://www.debian.org/mirror/list-non-US">
<citetitle>http://www.debian.org/mirror/list-non-US</citetitle>
</ulink> there are
<literallayout>
ftp://ftp.wa.au.debian.org/debian-non-US/
http://ftp.wa.au.debian.org/debian-non-US/

ftp://ftp.au.debian.org/debian-non-US/
http://ftp.au.debian.org/debian-non-US/

ftp://mirror.aarnet.edu.au/debian-non-US/
http://mirror.aarnet.edu.au/debian-non-US/

ftp://ftp.monash.edu.au/pub/linux/debian-non-US/
http://ftp.monash.edu.au/pub/linux/debian-non-US/

ftp://ftp.progsoc.uts.edu.au/pub/Linux/debian-non-US/
http://ftp.progsoc.uts.edu.au/pub/Linux/debian-non-US/

ftp://ftp.uwa.edu.au/mirrors/linux/debian-non-US/

ftp://mirror.eftel.com/debian-non-US/
http://mirror.eftel.com/debian-non-US/

ftp://mirror.pacific.net.au/debian-non-US/
http://mirror.pacific.net.au/debian-non-US/

ftp://ftp.iinet.net.au/debian/debian-non-US/
http://ftp.iinet.net.au/debian/debian-non-US/

ftp://debian.ihug.com.au/debian-non-US/
http://debian.ihug.com.au/debian-non-US/

ftp://debian.vicnet.net.au/debian-non-US/
http://debian.vicnet.net.au/debian-non-US/ 
</literallayout>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to create a temporary file?
</para>
</question>
<answer>
<para>
Using Korn shell and a combination of current program and current process id
<programlisting><![CDATA[
# create a unique temporary file
tempfile=/tmp/${0##*/}.$$
debug "Using tempfile ${tempfile}"
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to remove control characters from a file?
</para>
</question>
<answer>
<para>
The problem is you have unwanted hex characters in a file.
How can they be removed? 
</para>
<para>
Firstly, the value of the characters can be use found using
<command>less(1)</command>.
</para>
<para>
Or use <command>od(1)</command> to see *what* the control characters are
<programlisting><![CDATA[
od -cx my_file| less
]]></programlisting>
</para>
<para>
These characters can be replaced using sed(1)
<programlisting><![CDATA[
sed 's/\x00//g' my_file > my_new_file
]]></programlisting>
</para>
<para>
But, if you think it is just bad control characters - then you can short cut
this using
<programlisting><![CDATA[
sed '' my_file > my_new_file
]]></programlisting>
What <command>sed(1)</command> does here is print to stdout
(<filename>my_new_file</filename>) only non-control characters.
</para>
<para>
There are some decent hex editors on Linux.  From the command line there is a
tool <command>xxd(1)</command> that will make hex dump to ASCII and the ability to
reverse the process.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to read emails formatted in HTML?
</para>
</question>
<answer>
<para>
Add the following into <filename>/etc/mailcap</filename> or <filename>~/.mailcap</filename>
<programlisting><![CDATA[
text/html; /usr/bin/lynx -dump -force_html '%s'; copiousoutput; description=HTML Text; nametemplate=%s.html
]]></programlisting>
You can also use a web browser if you are running X
<programlisting><![CDATA[
text/html; /usr/bin/firefox '%s'; description=HTML Text; test=test -n "$DISPLAY";  nametemplate=%s.html
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to resize gnucash reports saved to HTML?
</para>
</question>
<answer>
<para>
Apply stylesheet with
<programlisting><![CDATA[
<STYLE TYPE="text/css">
    TD { font-size: 8pt; }
</STYLE>
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to edit recently viewed gnucash files?
</para>
</question>
<answer>
<para>
See <filename>$HOME/.gconf/apps/gnucash/history/%gconf.xml</filename>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How do you (re)set local timezone?
</para>
</question>
<answer>
<para>
For Debian based systems use <command>dpkg-reconfigure(1)</command>, as in
<programlisting><![CDATA[
dpkg-reconfigure tzdata
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
Hint on how to unpack an <filename>TAR</filename> archives.
</para>
</question>
<answer>
<para>
You don't need to move a <filename>.tar</filename> archive file to a certain
directory because it happens to be in the directory you want to extract it into.
Instead, unpack a <filename>.tar</filename> archive file into any directory you
like using the -C option
<programlisting><![CDATA[
tar xvf -C tmp/a/b/c newarc.tar.gz
]]></programlisting>
Making a habit of using -C is preferable to moving the archive file to where
you want to unpack it, changing to that directory, and only then extracting its
contents - especially if the archive file belongs somewhere else.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to read a Java style properties file from a shell script?
</para>
</question>
<answer>
<para>
To search for a properties value called "key", use
<programlisting><![CDATA[
KEY=`awk 'BEGIN{FS="="}; /^key/ {printf("%s", $2); exit}' java.properties`
]]></programlisting>
</para>
<para>
The problem is if there is embedded spaces. In which case use
<programlisting><![CDATA[
`awk 'BEGIN{FS="[ \t]*=[ \t]*"}; /^[ \t]*key/ {printf("%s", $2); exit}' java.properties`
]]></programlisting>
</para>
<para>
Here is a little test program for the above process
<programlisting><![CDATA[
# create a temporary properties file
tempproperties=/tmp/${0##*/}.$$
echo "key1=value1"      >  $tempproperties
echo "key2 = value2"    >> $tempproperties
echo "key3= value3"     >> $tempproperties
echo "key4 =value4"     >> $tempproperties
echo " key5 = value5"   >> $tempproperties

key1=`awk 'BEGIN{FS="[ \t]*=[ \t]*"}; /^[ \t]*key1/ {printf("%s", $2); exit}' $tempproperties`
key2=`awk 'BEGIN{FS="[ \t]*=[ \t]*"}; /^[ \t]*key2/ {printf("%s", $2); exit}' $tempproperties`
key3=`awk 'BEGIN{FS="[ \t]*=[ \t]*"}; /^[ \t]*key3/ {printf("%s", $2); exit}' $tempproperties`
key4=`awk 'BEGIN{FS="[ \t]*=[ \t]*"}; /^[ \t]*key4/ {printf("%s", $2); exit}' $tempproperties`
key5=`awk 'BEGIN{FS="[ \t]*=[ \t]*"}; /^[ \t]*key5/ {printf("%s", $2); exit}' $tempproperties`

test "$key1" != "value1" && echo "expected \"value1\" got \"$key1\""
test "$key2" != "value2" && echo "expected \"value2\" got \"$key2\""
test "$key3" != "value3" && echo "expected \"value3\" got \"$key3\""
test "$key4" != "value4" && echo "expected \"value4\" got \"$key4\""
test "$key5" != "value5" && echo "expected \"value5\" got \"$key5\""

echo "key1=$key1"
echo "key2=$key2"
echo "key3=$key3"
echo "key4=$key4"
echo "key5=$key5"

/bin/rm -f $tempproperties
]]></programlisting>
</para>
<para>
Another way to do this is
<programlisting><![CDATA[
# general pattern to search for a key from a properties file
value=$(grep "^key1.*=" ${propertiesFile} | sed 's/^.*=//')
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to remove empty lines from a file?
</para>
</question>
<answer>
<para>
In <command>vim(1)</command> this can be done globally using
<programlisting><![CDATA[
:%g/^$/d
]]></programlisting>
</para>
<para>
A related problem is to remove white space from a line. 
To remove leading white space use
<programlisting><![CDATA[
:%s/^\s\+//
]]></programlisting>
To remove trailing white space use
<programlisting><![CDATA[
:%s/\s\+$//
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
Why do I get the error <quote>Host or domain name not found</quote>?
</para>
</question>
<answer>
<para>
<command>Postfix(1)</command> is using DNS to lookup the outgoing address
specified in <filename>/etc/mailname</filename>.  Disable DNS lookups by adding
this line to <filename>/etc/postfix/main.cf</filename>
<programlisting><![CDATA[
disable_dns_lookups = yes
]]></programlisting>
This will allow mail to be correctly delivered to users on localhost.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
What programs understand tabs?
</para>
</question>
<answer>
<para>
Scripting languages (Perl, awk, etc), can parse and write tab-separated data.
The following table lists some other Linux utilities that handle tabs.
<table frame='all'><title>Some utilities that understand tabs</title>
<tgroup cols='2' align='left' colsep='1' rowsep='1'>
<thead>
<row>
  <entry>Utility</entry>
  <entry>Description</entry>
</row>
</thead>
<tbody>
<row>
  <entry>cat(1)</entry>
  <entry>Concatenate files and print on the standard output</entry>
</row>
<row>
  <entry>cut(1)</entry>
  <entry>Remove sections from each line of files</entry>
</row>
<row>
  <entry>echo(1), printf(1)</entry>
  <entry>Display a line of text</entry>
</row>
<row>
  <entry>expand(1), unexpand(1)</entry>
  <entry>Converts between TABS and spaces</entry>
</row>
<row>
  <entry>paste(1)</entry>
  <entry>Merge lines of files</entry>
</row>
<row>
  <entry>sed(1)</entry>
  <entry>Stream editor for filtering and transforming text</entry>
</row>
<row>
  <entry>sort(1)</entry>
  <entry>Sort lines of text files</entry>
</row>
</tbody>
</tgroup>
</table>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to check and repair a file system?
</para>
</question>
<answer>
<para>
Determine which file system you want to check.  This can be done by inspecting
<filename>/etc/fstab</filename>.  Use <command>fsck(8)</command>.  
<programlisting><![CDATA[
fsck.vfat -vfalt /dev/sdb1
]]></programlisting>
Alternatively, for <filename>ext2</filename> and <filename>ext4</filename> file systems try
<programlisting><![CDATA[
e2fsck -vfp /dev/sdb1
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to switch to a virtual screen?
</para>
</question>
<answer>
<para>
Normally you can do this by pressing <command>CTL-ALT-FNv</command>, where v is
the virtual screen to switch to.  However, if this keyboard mapping is not supported 
then use <command>chvt(1)</command>.  You will need root access to invoke this.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to re-map keyboard?
</para>
</question>
<answer>
<para>
This is done using <command>xbindkeys(1)</command>. Assume you want to re-map
F5 to start a X terminal.
<orderedlist>
<listitem>
<para>
Create a xbindkeys configuration file
<screen>
HOME:~$ xbindkeys -d > ~/.xbindkeysrc
</screen>
</para>
</listitem>
<listitem>
<para>
Determine what the keycode is for F5 
<screen>
HOME:~$ xbindkeys -k
Press combination of keys or/and click under the window.
You can use one of the two lines after "NoCommand"
in $HOME/.xbindkeysrc to bind a key.
"(Scheme function)"
    m:0x10 + c:237
    Mod2 + XF86KbdBrightnessDown
</screen>
</para>
</listitem>
<listitem>
<para>
Edit this file, adding the following lines
<screen>
# F5 = xterm
"xterm -sb -right"
    m:0x10 + c:237
</screen>
</para>
</listitem>
<listitem>
<para>
xbindkeys is invoked on X window startup by adding this into <filename>~/.xprofile</filename>
<screen>
# use my keyboard bindings
nice xbindkeys &amp;
</screen>
</para>
</listitem>
</orderedlist>
Re-start X window session, and F5 should now start a X11 terminal.
Finally, to see a summary of keyboard bindings use <command>xbindkeys_show</command>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to support the Mac wired 220 aluminium keyboard?
</para>
</question>
<answer>
<para>
To fully support this keyboard you may want to re-map to support the code changes
<itemizedlist>
<listitem>
<para>
Where is the <command>insert</command> key?
</para>
<para>
This can be accessed by pressing <command>fn + return</command>.
</para>
</listitem>
<listitem>
<para>
Where is the <command>num-lock</command> key?
</para>
<para>
This is mapped to <command>clear</command> on the number pad.
</para>
</listitem>
<listitem>
<para>
Where are the function keys?
</para>
<para>
By default the <command>fn</command> key has priority (priority=0).  So, to
access <command>F8</command> for example, press <command>fn + F8</command>.
This can be re-mapped to give the function key priority. So function keys are
used as first key. Pressing <command>F8</command> key will behave like a
<command>F8</command>. Pressing <command>fn + F8</command> will act as special
key (play/pause).  To change to this key priority
    <orderedlist>
    <listitem>
    <para>
    Add the following line to <filename>/etc/modprobe.d/hid_apple.conf</filename>
    <programlisting><![CDATA[
    options hid_apple fnmode=2
    ]]></programlisting>
    </para>
    </listitem>
    <listitem>
    <para>
    Run <command> update-initramfs -u </command>
    </para>
    </listitem>
    <listitem>
    <para>
    Reboot.
    </para>
    </listitem>
    </orderedlist>
</para>
</listitem>
</itemizedlist>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to list subversion repository projects?
</para>
</question>
<answer>
<para>
Using just <command>svn(1)</command> and <command>awk(1)</command>
<programlisting><![CDATA[
svn list -R file:///var/lib/svn/frank/trunk |awk -F/ '$NF ~ /^$/ && NF <= 3'
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to set subversion keywords?
</para>
</question>
<answer>
<para>
Using just <command>svn(1)</command>
<programlisting><![CDATA[
svn propset svn:keywords "Id" *.sgml
]]></programlisting>
Commit the changed files
<programlisting><![CDATA[
svn ci -m "* applied svn keyword substitution" *.sgml
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to save a subset of a PDF document?
</para>
</question>
<answer>
<para>
This example uses <command>pdftops(1)</command> to specify a range of pages to
print.  The input format is PDF, and the result is a PostScript file
<programlisting><![CDATA[
pdftops -f 1 -l 2 document.pdf document.ps
]]></programlisting>
Use <command>gv(1)</command> to view results.
</para>
<para>
Another way to split a PDF document is to use <command>pdftk(1)</command>.  For
example to split an 8 page document into pages 1-7, and page 8 use
<programlisting><![CDATA[
pdftk document.pdf cat 1-7 output document-1-7.pdf
]]></programlisting>
To split a document into seperate pages you first need to know how many there are in the document,
<programlisting><![CDATA[
PAGES=$(pdfinfo document.pdf| awk '/Pages:/ {print $2}')
]]></programlisting>
Then split using
<programlisting><![CDATA[
for (( p=1; p <= $PAGES; p++)); do \
	pdftk document.pdf cat $p output document.pdf-$p.pdf; \
done
]]></programlisting>
Another way to split a document is by using <command>gs(1)</command>
<programlisting><![CDATA[
gs -sDEVICE=pdfwrite -dNOPAUSE -dQUIET -dBATCH -dFirstPage=1 -dLastPage=1 -o document-1-7.pdf document.pdf
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to combine a number of PDF files?
</para>
</question>
<answer>
<para>
Ghostscript <command>gs(1)</command> gives you the power to combine files, convert files, and much more,
all from the command line. To combine several input files into one
combined PDF using Ghostscript
<programlisting><![CDATA[
gs -sDEVICE=pdfwrite -dSAFER -dNOPAUSE -dBATCH -o combined.pdf first.pdf second.pdf third.pdf [...]
]]></programlisting>
Equivalently, using the -o option
<programlisting><![CDATA[
gs -sDEVICE=pdfwrite -dSAFER -o combined.pdf first.pdf second.pdf third.pdf [...]
]]></programlisting>
</para>
<para>
If this doens't give the results you want, try <command>psmerge(1)</command>
<programlisting><![CDATA[
psmerge -ocombined.pdf first.pdf second.pdf third.pdf [...]
]]></programlisting>
This gives good results, but the result file size is larger than that achieved with Ghostscript.
</para>
<para>
Another method uses the <command>pdfjoin(1)</command> command
<programlisting><![CDATA[
pdfjoin --outfile combined.pdf first.pdf second.pdf third.pdf [...]
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to scan a document and save as a PDF?
</para>
</question>
<answer>
<para>
If you use <command>xsane</command> to scan documents, it will save as a PDF.
However, the document saved in this format is often many megabytes larger than
it should be. Instead save as a <filename>PNM</filename> or Portable Any Map
document.
</para>
<para>
Convert scanned PNM to a PDF using <command>mogrify(1)</command>, from the
<command>ImageMagick(1)</command> command family: 
<programlisting><![CDATA[
mogrify -format pdf input.pnm
]]></programlisting>
Next, post process using Ghostscript <command>gs(1)</command>. 
<programlisting><![CDATA[
gs -sDEVICE=pdfwrite -dSAFER -ooutput.pdf input.pdf
]]></programlisting>
This results is a much better sized PDF document.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to copy a large amount of data?
</para>
</question>
<answer>
<para>
To copy from a source to some target directory using the <command>tar(1)</command>
<programlisting><![CDATA[
tar cvf - source_directory | ( cd target_directory && tar xBf - )
]]></programlisting>
This will fail if the target directory doesn't exist.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to indent a file in vim?
</para>
</question>
<answer>
<para>
Ensure the following are set in your <filename>.vimrc</filename>
<screen>
set expandtab         " don't use tabs use spaces to give consistent output
set tabstop=4         " change default tabs
set softtabstop=4     " how many spaces used when using TAB in insert mode
set shiftwidth=4      " change default shift widt
set shiftround        " indent to nearest tabstop
set textwidth=0       " don't wrap words by default
set autoindent        " always set autoindenting on
set smartindent       " do smart autoindenting when starting a new line
set cinoptions+=j1    " indentation of java anonymous classes

:if has("autocmd")
    " Enabled file type detection
    " Use the default filetype settings. If you also want to load indent files
    " to automatically do language-dependent indenting add 'indent' as well.
    filetype plugin indent on
:endif " has ("autocmd")
</screen>
</para>
<para>
Restart vim. Now, to indent a file in vim use the command <command>gg=G</command>.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to synchronise files in a directory on a USB stick to a local directory?
</para>
</question>
<answer>
<para>
Using <command>rsync(1)</command>
<programlisting><![CDATA[
rsync -riW /media/verbatim/oss/dev/graph /home/frank/dev
]]></programlisting>
This will recursively iterate through the source directory, showing files
changed. Note that the target does not include the source directory.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
Why do I get an error when running <command>showrgb(1)</command>?
</para>
</question>
<answer>
<para>
If you get this error message when showing the RGB colour program
<screen>
showrgb:  unable to open rgb database "/usr/share/X11/rgb"
</screen>
This is likely due to a broken symbolic link.  Fix it with
<programlisting><![CDATA[
ln -s /etc/X11/rgb.txt /usr/share/X11
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to import a project directory to subversion?
</para>
</question>
<answer>
<para>
Assuming the project directory is a subdirectory of the current directory, use
the following command
<programlisting><![CDATA[
svn import file:///var/lib/svn/home/project -m "initial import"
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to move a subversion project to a different location?
</para>
</question>
<answer>
<para>
I had incorrectly loaded a project into the wrong path.
I wanted under trunk, but put it under home.  How do I move it?
Simple
<programlisting><![CDATA[
svn mv file:///var/lib/svn/home/project file:///var/lib/svn/home/trunk/project
]]></programlisting>
List the results using
<programlisting><![CDATA[
svn list file:///var/lib/svn/home/trunk
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to determine the model and revision of your video chipset?
</para>
</question>
<answer>
<para>
Use the <command>lspci(8)</command> command. Type
<programlisting><![CDATA[
lspci -v | grep VGA
]]></programlisting>
This will display the required information. On my system the output looks like this
<screen>
01:00.0 VGA compatible controller: nVidia Corporation NV44 [GeForce 6200 TurboCache(TM)] (rev a1)
</screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to send an email attachment?
</para>
</question>
<answer>
<para>
This is how to send mail attachments using commands,
<command>uuencode(1)</command> to prepare the attachment, then sending via
<command>mailx(1)</command>
<orderedlist> 
<listitem> 
<para>
<screen>
uuencode /home/ccuser/d364875/reports/buildtimes.xml > attachment
</screen>
</para>
</listitem> 
<listitem> 
<screen>
mailx -s "attachment.zip" frankhjung@company.dom &lt; attachment
</screen>
</listitem> 
</orderedlist> 
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to set the volume name of a device?
</para>
</question>
<answer>
<para>
Use <command>tune2fs(8)</command>
<programlisting><![CDATA[
tune2fs -L MYNAME /dev/sdb2
]]></programlisting>
List device information using either <command>tune2fs(8)</command>, or <command>volname</command>
<programlisting><![CDATA[
tune2fs -l /dev/sdb2
volname /dev/sdb2
]]></programlisting>
</para>
</answer>
</qandaentry>


<qandaentry>
<question>
<para>
How to efficiently search through many files?
</para>
</question>
<answer>
<para>
Use the following
<programlisting><![CDATA[
find /dir/path -type f -print0 | xargs -0 grep -Hi "search term"
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to use MPlayer to record live streams from the Internet
</para>
</question>
<answer>
<para>
All you need to record a live stream from the web is
<command>MPlayer(1)</command>. Use the -dumpstream argument to capture a MMS,
ASF or Live WMV stream to a file called <filename>stream.dump</filename>.
</para>
<para>
For example
<programlisting><![CDATA[
mplayer -dumpstream mmsh://streamer3.carnation.hu/mtvonlinem2?MSWMExt=.asf
]]></programlisting>
will create a stream.dump file that you can later rename to my_recorded_stream.wmv.
</para>
<para>
Note This will not work with Flash-powered streams.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to run a command periodically, forever?
</para>
</question>
<answer>
<para>
Try the <command>watch(1)</command> command.  For example,
<programlisting><![CDATA[
watch -n 5 command
]]></programlisting>
Will run a command every 5 seconds.
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to manage podcasts?
</para>
</question>
<answer>
<para>
<ulink url="http://podracer.sourceforge.net/">Podracer</ulink> was written by
<author><firstname>Lorenzo</firstname><surname>Taylor</surname></author>. It is
a simple to use, command line tool that uses only two plain text configuration
files
<screen><![CDATA[
$HOME/.podracer/podracer.conf - configure podracer behaviour
$HOME/.podracer/subscriptions - list of subscriptions
]]></screen>
</para>
<para>
<variablelist>
<varlistentry>
    <term>Configuration</term>
    <listitem>
        <para>
        This file is used to customise podracers download behaviour. With sane
        defaults, the only settings that I changed were, 
        <variablelist>
        <varlistentry>
            <term>poddir</term>
            <listitem>
                <para>
                the default root location to save podcasts into 
                </para>
            </listitem>
        </varlistentry>
        </variablelist>
        And two other entries indicating where the log files are to be recored.
        </para>
    </listitem>
</varlistentry>
<varlistentry>
    <term>Subscriptions</term>
    <listitem>
        <para>
        Like the name suggests this a plain text file listing the podcasts you
        subscribe to. The format is simple,
        <screen>
        RSS_feed target_directory_relative_to_poddir 
        </screen>
        As this is a plain text file, where comments can be added by appending
        <literal>#</literal> to a line, it becomes a useful historical record
        of podcasts I listen to. 
        </para>
    </listitem>
</varlistentry>
<varlistentry>
    <term>Maintenance</term>
    <listitem>
        <para>
        To get the most out of podracer, schedule jobs to run during off-peaks times.
        <programlisting><![CDATA[
# update podcasts (run every day at 03:03)
3 3 * * * podracer 
        ]]></programlisting>
        To effortlessly manage podcasts so I don't become overrun by them, I
        keep only one months worth. This is managed by another crontab entry,
        <programlisting><![CDATA[
# clean-up old podcasts
@daily find $HOME/music/podcasts/ -name '*.mp3' -type f -mtime +31 -exec rm -v {} \;
        ]]></programlisting>
        </para>
    </listitem>
</varlistentry>
</variablelist>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to determine your public IP address?
</para>
</question>
<answer>
<para>
<variablelist>
<varlistentry>
    <term>Using <command>curl(1)</command></term>
    <listitem>
        <para>
            <screen>
curl ifconfig.me
            </screen>
        </para>
   </listitem>
</varlistentry>
<varlistentry>
    <term>Using <command>wget(1)</command></term>
    <listitem>
        <para>
            <screen>
wget -qO- ifconfig.me/ip
            </screen> 
        </para>
   </listitem>
</varlistentry>
</variablelist>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to export a Git archive?
</para>
</question>
<answer>
<para>
The simplest method is to use
<programlisting>git archive -o latest.zip HEAD</programlisting>
And here is a script to archive a git repositories relative to current
directory,
<programlisting><![CDATA[
#!bash

basedir=$(pwd)
for f in $(find . -maxdepth 1 -type d); do
    if [ -d $f/.git ]; then
        echo -n "archiving $f ..."
        cd $f
        git archive -o $basedir/$f.zip HEAD
        cd $basedir
        echo " done!"
    else
        echo "ignoring $f"
    fi
done
]]></programlisting>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
How to run command to show on alternate machine?
</para>
</question>
<answer>
<para>
If <command>xhost(1)</command> doesn't work, try this
<screen><![CDATA[
echo $DISPLAY                  # you'll be needing this value 3 lines below
sudo -i                        # or "su -" on older Slackwares
xauth merge ~alien/.Xauthority # use your own username here instead of "alien"
export DISPLAY=:0.0            # use the value of DISPLAY you've seen 3 lines before
]]></screen>
</para>
</answer>
</qandaentry>

<qandaentry>
<question>
<para>
Show some list directory (ls) shortcuts.
</para>
</question>
<answer>
<para>
The <command>ls(1)</command> command is one of the most often run commands. So,
here is a list of shortcuts and hints to get the most out of it.
</para>
<para>
First I use a number of shell aliases:
   <simplelist type='horiz' columns='2'>
      <member>,</member> 
      <member>ls -Fal</member> 
      <member>l</member> 
      <member>ls -lF --show-control-chars</member> 
      <member>la</member> 
      <member>ls -d .[a-zA-Z]*</member> 
      <member>ls</member> 
      <member>ls --color=auto</member> 
   </simplelist>
</para>
<para>
Next we set default colours. Typically I use a dark background, and the
defaults are set up for white background. Why is that? This requires remapping
some colours so the become more legible. This is done by setting the environment varible LS_COLORS. Here are my defaults:
<screen><![CDATA[
rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arj=01;31:*.taz=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.zip=01;31:*.z=01;31:*.Z=01;31:*.dz=01;31:*.gz=01;31:*.lz=01;31:*.xz=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31:*.tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.war=01;31:*.ear=01;31:*.sar=01;31:*.rar=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.jpg=01;35:*.jpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.webm=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.axv=01;35:*.anx=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=00;36:*.au=00;36:*.flac=00;36:*.mid=00;36:*.midi=00;36:*.mka=00;36:*.mp3=00;36:*.mpc=00;36:*.ogg=00;36:*.ra=00;36:*.wav=00;36:*.axa=00;36:*.oga=00;36:*.spx=00;36:*.xspf=00;36:
]]></screen>
</para>
</answer>
</qandaentry>

<!-- to add a new FAQ entry

<qandaentry>
<question>
<para>
The question.
</para>
</question>
<answer>
<para>
The answer.
</para>
</answer>
</qandaentry>

-->

</qandaset>