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System & Process Status
at Execute commands later.
badblocks Searches a device for bad blocks.
bg Resume a suspended job in the background.
chage Change user password expiry information.
chgrp Change file group.
chown Change file owner.
chpasswd Update passwords in batch mode.
chroot Run command or interactive shell with special root directory.
crontab Automate commands.
date Set or display the current date and time.
df Show free disk space.
du Show disk usage.
env Show environment variables.
fdisk Partition a hard disk.
fg Resume a suspended job in the foreground and make it the current job.
finger Display information about users.
fuser Checks to see what processes and users have open files.
free Show total memory, used memory, and free memory.
gpasswd Set a password for a group.
groupadd Create new group account.
groupdel Delete a group.
groupmod Modify a group.
groups Show what groups a user is part of.
hdparm Get disk information.
host Show IP address of a domain name.
htpasswd Set usernames and passwords for your web server.
jobs Show jobs running in the background.
kill Terminate a running command.
killall Kill processes by command name.
last List logins and reboots.
lastlog Show the last login times for system accounts.
lsmod List loaded modules.
logrotate Manipulate log files.
netstat Shows active sockets.

ps Show processes.
reboot Reboot your server.
shutdown Shut down your server.
stty Set or display terminal settings.
top Show information about the most cpu-intensive applications.
uname Determine OS name, version and machine name.
useradd Add a new Linux user.
usermod Modify a Linux user (change login name).
userdel Delete an existing Linux user.
vmstat List information on memory usage.
who Show who is logged on.
whoami Show who is the current user.
Text Processing
awk Search for a pattern within a file using regular expression.
cut Select columns for display.
ex Line editor underlying vi.
fmt Produce roughly uniform line lengths.
join Join lines of two files on a common field.
nawk New version of awk (patter n-matching language for textual database files).
passwd Set your login password.
paste Merge columns or switch order.
sed Stream editor is used to perform basic text transformations.
sort Sort or merge files.
tr Translate (redefine) characters.
uniq Find repeated or unique lines in a file.
vi Visual text editor.
xargs Process many arguments in manageable portions.

The shell keeps a history of recent commands. You can view previous shell commands by typing in history. The following example shows a partial listing of past command history.

959 history
960 PATH=$PATH:/sbin:/usr/sbin
961 PS1='\! \u \w % '
962 su
963 ls tar/Z*
965 ls -alh
966 cd ~/mysql5
967 bin/mysql -uroot -pxxxxxx

To repeat a command in history, type in the command number from the list preceding with an exclamation symbol (!), for example !965 is equivalent to ls -alh, or you can use the up and down arrow key to get to a particular past command quickly.

Most commands show the output on the screen. You can use standard Linux redirection to capture the output to a file for later viewing.
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