From PCLinuxOShelp Knowledge Base
Index of Linux Commands
These represent only a fraction of the total number of standard commands typically included in Linux and other Unix-like operating systems.
alias: allows launching of any command or combination of commands by using a preset character or series of characters.
apropos: displays a list of all topics in the built-in user manual that are related to the subject of a query.
bzip2: used for compressing and decompressing files.
cat: (short for concatenate) has three related functions with regard to text files: displaying them, combining copies of them and creating new ones.
cd: changes directories.
clear: removes all previous commands and output from consoles and terminal windows.
cp: copies files and directories.
df: reports the amount of space used and available on currently mounted filesystems.
dmesg: reads the kernel messages.
du: shows the sizes of directories and files.
fdformat: performs low-level formatting of floppy disks.
file: classifies filesystem objects.
free: provides information about unused and used memory and swap space.
grep: searches text.
head: by default reads the first ten lines of text.
hostname: shows or sets a computer's host name and domain name.
kdesu: opens KDE su, the graphical front end for the su command.
kill: terminates stalled processes without having to log out or reboot.
killall: terminates all processes associated with programs whose names are provided to it as arguments.
locate: finds files and directories.
man: formats and displays the built-in manual pages.
mkbootdisk: creates an emergency boot floppy.
mkdir: creates new directories.
mkfs: creates a filesystem on a disk or on a partition thereof.
mv: renames and moves files and directories.
ps: (short for process status) lists the currently running processes and their process identification numbers (PIDs).
pstree: displays the processes on the system in the form of a tree diagram.
pwd: (short for present working directory) displays the full path to the current directory.
reboot: restarts a computer without having to turn the power off and back on.
rm: deletes the specified files and directories.
rmdir: deletes the specified empty directories.
runlevel: reports the current and previous runlevels.
shred: destroys files.
spell: checks spelling.
strings: returns each string of printable characters in files.
su: (short for substitute user) changes a login session's owner without the owner having to first log out of that session.
tail: by default reads the final ten lines of text.
tar: converts a group of files into an archive.
touch: the easiest way to create new, empty files.
tr: translates or deletes characters.
unalias: removes entries from the current user's list of aliases.
uname: provides basic information about a system's software and hardware.
uptime: shows the current time, how long the system has been running since it was booted up, how many user sessions are currently open and the load averages.
w: shows who is logged into the system and what they are doing.
wc: by default counts the number of lines, words and characters that are contained in text.
whatis: provides very brief descriptions of command line programs and other topics related to Unix-like operating systems.
whereis: locates the binary, source code and man page for any specified program.
whoami: returns the user name of the owner of the current login session.