1. Can I execute a command(s) when a certain or any user logs in?
2. How can I find a file on my system?
3. How can I find certain words in files on my system?
4. How do I decompress a .tar, .tar.gz or a .tgz file achive?
5. How do I create a tar file achive?
6. How do I set the blank time of my screensaver in console?
7. How can I find and replace certain words in files?
8. How do I ignor system messages at login?
9. Can I make a text version of a man page?
10. Can I ls just directorys?
11. How do I read a floppy disk in my A:\ drive?
12. How do I read my Windows partiton?
13. How can I tell what filesystems my kernel supports?
14. I just made changes to my /etc/profile. Do I have to reboot?
15. I just made changes to my ~/.bash_profile. Do I have to reboot?
16. How do I understand what those Linux Signal Errors mean?
17. How do I decompress a .bz2 file archive?
18. How do I list the number of files in the current directory?
19. How do I list the number of subdirectories in the current directory?
20. I cat a binary file and now my tty is unreadable. How do I fix this?
21. How do I get back to the last directory I was in?
22. How can I make a quick timer script?
23. How can I talk to a User on my Linux box?
24. How can I talk to all the Users at once on my Linux box?
25. How can I count the lines in a file?
26. How can I divide a number?
27. How do I stop a crontab from emailing me?
28. How can I have the results of a crontab be emailed to a User?
29. How do I list files by size?
30. How do remove blank lines from a file?
31. How do I Add, Edit or Delete a crontab?
32. How can I get the number of files (inodes) in all the directories in the current directory?
33. How can I check the processes of two or more users?
34. I have a command aliased with switches. How do I unalias it quickly?
35. How do I kill a user and thier processes?
36. How do a split up a file so that it will fit on floppys?
37. How do I turn my numberlock key on at bootup?
38. How can I list loaded modules currently in use?
39. How do I list the contents of a tar or tar.gz file?
40. How do prevent pico from wrapping long lines?
41. How can I find out how much memory I am using?
42. How can I check how much space I am using on my hard drive(s)?
43. How can I check how much hard drive space a certain directory is using?
44. How do I check my email with fetchmail?

Q. Can I execute a command(s) when a certain or any user logs in?
A. Sure! Basicly add the following to '/etc/profile'.

# EXAMPLE:

USER_NAME=`whoami`

case "$USER_NAME" in
       "root") command;;
     "shelly") command;;
            *) command;;
esac

# The "*" asterisk assigns the default action.

# SYNTAX:

     case "$VARIABLE" in
     value1) command ;;
     value2) command
             command
             command ;;
     value3) command
             command ;;
     value4) command ;;
          *) command
             command ;;
esac

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Q. How can I find a file on my system?
A. Just do this at your prompt.

find DirectoryName -name FileName -printf "Found file: %p \n"

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Q. How can I find certain words in files on my system?
A. Just do this at your prompt.

find DirectoryName -type f -printf "%p " | xargs egrep -i "String" | less

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Q. How do I decompress a .tar, .tar.gz or a .tgz file achive?
A. Its simpily...

tar -xzvf for a .tar.gz or .tgz file.

# or...

tar -xvf for a .tar file.

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Q. How do I create a tar file achive?
A. Its simpily...

tar -cvf FileOrDirectory.tar FileOrDirectory

# or to gzip it at the same time...

tar -czvf FileOrDirectory.tgz FileOrDirectory

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Q. How do I set the blank time of my screensaver in console?
A. Usally set in  /etc/rc.d/rc.M

# EXAMPLE:

# To make your screen blanks after 15 minutes of idle time.

/bin/setterm -blank 15

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Q. How can I find and replace certain words in files?
A. Just do this at your prompt.

perl -e "s/old_string/new_string/g;" -pi.save $(find DirectoryName -type f)

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Q. How do I ignor system messages at login?
A. Just do this at your prompt.

touch ~/.hushlogin

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Q. Can I make a text version of a man page?
A. Just do this at your prompt.

man ManName | col -b > ManName.txt

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Q. Can I ls just directorys?
A. Just do this at your prompt.

ls -l | grep "^d"

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Q. How do I read a floppy disk in my A:\ drive?
A. Very simply.
mkdir /floppy; mount -t msdos /dev/fd0 /floppy

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Q. How do I read my Windows partiton?
A. At your Linux prompt type this.

mkdir /win; mount -t vfat /dev/hda1 /win

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Q. How can I tell what filesystems my kernel supports?
A. Just type this at you Linux command prompt.

cat /proc/filesystems

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Q. I just made changes to my /etc/profile. Do I have to reboot?
A. No you don't if you do this at your prompt.

source /etc/profile

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Q. I just made changes to my ~/.bash_profile. Do I have to reboot?
A. No you don't if you do this at your prompt.

source ~/.bash_profile

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Q. How do I understand what those Linux Signal Errors mean?
A. They are listed in the man pages if you know where to look. Try...

man 7 signal

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Q. How do I decompress a .bz2 file archive?
A. Its simpily...

bzip2 -dv FileName.bz2

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Q. How do I list the number of files in the current directory?
A. At your Linux prompt type

ls -la |grep "^-" |awk 'END {print "Number of files: " NR}'

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Q. How do I list the number of subdirectories in the current directory?
A. At your Linux prompt type

ls -la |grep "^d" |awk 'END {print "Number of directories: " NR}'

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Q. I cat a binary file and now my tty is unreadable. How do I fix this?
A. Do this at your Linux prompt

<Control>+v <Escape>+c

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Q. How do I get back to the last directory I was in?
A. Just type this at your Linux prompt

cd -

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Q. How can I make a quick timer script?
A. Create and run this quick BASH script

#!/bin/sh

tput clear
while tput home; do
        date
        sleep 1
done

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Q. How can I talk to a User on my Linux box?
A. At your Linux prompt

who
write <the user name> <the tty>
<message>
<message>
<Control>+d

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Q. How can I talk to all the Users at once on my Linux box?
A. At your Linux prompt

wall
<message>
<message>
<Control>+d

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Q. How can I count the lines in a file?
A. At your Linux Prompt

wc -l <file name>

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Q. How can I divide a number?
A. At your Linux Prompt

echo "1234567 / 2" | bc

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Q. How do I stop a crontab from emailing me?
A. Just add this to the end of the crontab line

> /dev/null 2>&1

For example:

# Run my_script every 5 minutes
*/5 * * * * /usr/local/bin/my_script > /dev/null 2>&1

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Q. How can I have the results of a crontab be emailed to a User?
A. Just use mailx

Syntax: [command or script] | mailx -s "Subject line" [EMAIL]

For example:

# Run date_script every 20 minutes
*/20 * * * * /bin/date_script | mailx -s "Date script cron" root

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Q. How do I list files by size?
A. At your Linux prompt type

ls -l | sort -n +4

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Q. How do remove blank lines from a file?
A. Just use sed

sed -e '/^$/d' <file with blank lines > <new file>

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Q. How do I Add, Edit or Delete a crontab?
A. At the command prompt type

crontab -e

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Q. How can I get the number of files (inodes) in all the directories in the current directory?
A. Use this find command

find . -xdev -type d -exec /bin/echo -n {} \; -exec sh -c "ls {} | wc -l" \;

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Q. How can I check the processes of two or more users?
A. Just use egrep

ps -aux | egrep '<user one>|<user two>'

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Q. I have a command aliased with switches. How do I unalias it quickly?
A. Just preceed the command with a backslash '\'

For example if you have an alias:

alias pico='pico -w -z'

Use:

\pico

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Q. How do I kill a user and thier processes?
A. This will work nicely

su - <user name> -c 'kill -9 -1'

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Q. How do a split up a file so that it will fit on floppys?
A. Use split:

split -b 1400000 <file name>

To reassemble use cat:

cat x* > <original file name>

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Q. How do I turn my numberlock key on at bootup?
A. Use setleds

# Example:

# Use the setleds program, for example (in /etc/rc.local
# or one of the /etc/rc.d/* files):

for t in 1 2 3 4 5 6 7 8
do
setleds +num < /dev/tty$t > /dev/null
done

# Alternatively, patch your kernel. You need to arrange
# for KBD_DEFLEDS to be defined to (1 << VC_NUMLOCK)
# when compiling drivers/char/keyboard.c.

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Q. How can I list loaded modules currently in use?
A. At your Linux prompt type:

lsmod

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Q. How do I list the contents of a tar or tar.gz file?
A. You can list the contents of a tar archive with the -t switch.
To list the contents of a .tar file type:

tar -tf filesname.tar

To list the contents of a .tar.gz file type:

tar -ztf filesname.tar.gz

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Q. How do prevent pico from wrapping long lines?
A. Start pico with:

pico -w

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Q. How can I find out how much memory I am using?
A. At your Linux prompt type:

free

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Q. How can I check how much space I am using on my hard drive(s)?
A. At your Linux prompt type:

df

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Q. How can I check how much hard drive space a certain directory is using?
A. At your Linux prompt type:

du -s <directory name>

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Q. How do I check my email with fetchmail?
A. Create a file called ~/.fetchmailrc containing

poll <mail server> proto pop3
user <user name> with pass <passwd> is <local user name> here

# Then set the correct permissions

chmod 600 ~/.fetchmailrc

# Then to fetch your email type

fetchmail

# Or to automaticly chech your email every so many seconds


fetchmail -d <number of seconds>

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