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
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"
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
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.
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
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
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)
Q. How do I ignor system messages at login?
A. Just do this at your prompt.
touch ~/.hushlogin
Q. Can I make a text version of a man page?
A. Just do this at your prompt.
man ManName | col -b > ManName.txt
Q. Can I ls just directorys?
A. Just do this at your prompt.
ls -l | grep "^d"
Q. How do I read a floppy disk in my A:\ drive?
A. Very simply.
mkdir /floppy; mount -t msdos /dev/fd0 /floppy
Q. How do I read my Windows partiton?
A. At your Linux prompt type this.
mkdir /win; mount -t vfat /dev/hda1 /win
Q. How can I tell what filesystems my kernel supports?
A. Just type this at you Linux command prompt.
cat /proc/filesystems
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
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
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
Q. How do I decompress a .bz2 file archive?
A. Its simpily...
bzip2 -dv FileName.bz2
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}'
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}'
Q. I cat a binary file and now my tty is unreadable. How do I fix this?
A. Do this at your Linux prompt
+v +c
Q. How do I get back to the last directory I was in?
A. Just type this at your Linux prompt
cd -
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
Q. How can I talk to a User on my Linux box?
A. At your Linux prompt
who
write
+d
Q. How can I talk to all the Users at once on my Linux box?
A. At your Linux prompt
wall
+d
Q. How can I count the lines in a file?
A. At your Linux Prompt
wc -l
Q. How can I divide a number?
A. At your Linux Prompt
echo "1234567 / 2" | bc
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
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
Q. How do I list files by size?
A. At your Linux prompt type
ls -l | sort -n +4
Q. How do remove blank lines from a file?
A. Just use sed
sed -e '/^$/d'
Q. How do I Add, Edit or Delete a crontab?
A. At the command prompt type
crontab -e
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" \;
Q. How can I check the processes of two or more users?
A. Just use egrep
ps -aux | egrep '|'
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
Q. How do I kill a user and thier processes?
A. This will work nicely
su - -c 'kill -9 -1'
Q. How do a split up a file so that it will fit on floppys?
A. Use split:
split -b 1400000
To reassemble use cat:
cat x* >
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.
Q. How can I list loaded modules currently in use?
A. At your Linux prompt type:
lsmod
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
Q. How do prevent pico from wrapping long lines?
A. Start pico with:
pico -w
Q. How can I find out how much memory I am using?
A. At your Linux prompt type:
free
Q. How can I check how much space I am using on my hard drive(s)?
A. At your Linux prompt type:
df
Q. How can I check how much hard drive space a certain directory is using?
A. At your Linux prompt type:
du -s
Q. How do I check my email with fetchmail?
A. Create a file called ~/.fetchmailrc containing
poll proto pop3
user with pass is 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
