commands and descriptions:
Commands are generally entered in this format: command -options argument(s). Options are similar to DOS switches like /? but instead of a slash require a hyphen instead. Some options may be used in combination with each other...example: ls -la.

fix this -
apt-get update - update list of packages
apt-get upgrade - upgrade installed packages
apt-get install <package>
apt-get remove <package>
apt-get dist-upgrade - upgrades system
apt-cache search <phrase>

adduser [username]
Begins the adduser wizard

alias
Displays aliases already set. Set an alias like so: alias ls='ls -F', temporarily or permanently with by adding to ~/.bashrc

apropos [keyword]
Searches whatis database for commands that match search criteria. "man -k" provides this same functionality

bg [job#]
Resumes suspended job (ctrl-z) in the background. If a job is not specified then the current job is resumed.

cal
Displays current month and year
cal [month as # or ##] [year as ####]
Displays the particular month of the year that was specified.
cal [year as ####]
Displays the entire monthly calendar for that particular year.

cat [file] 
Concatenate files and display to standard output (screen)
Options:

• cat -n [file] Number output lines
  

cd [directory]
Change directory. Works like the DOS cd command
"cd" Takes you to your home directory when no arguments are given
"cd .." Takes you up one to the parent directory of your current location
"cd ../.." Takes you up two parent directories, etc
"cd -" Returns to previous directory
"cd ~" Takes you to home directory
"cd ~resinblade" Takes you to specified user's home directory
"cd ~resinblade/dirname" Takes you to specified directory in user's home directory

cfdisk
Curses based fdisk-like utility

chage [username]
Manages user accounts password aging
Options:

• chage -l Lists password aging information
  
• chage -E [YYYY-MM-DD] Sets account expiration date
• chage -m [days] Sets minimum # of days before user is able to change password. A value of 0 means any time
• chage -M [days] Sets maximum # of days before a password change is mandatory. A value of 0 means the user will have to change his/her password before their next login
• chage -W [days] Sets # of days before a warning is issued to the user of an upcoming mandatory password change
  

chattr +(or - or =)[attribute] [file/directory]
Changes file attributes specified files.
Attributes:
a = append-only
A = no access time updates
c = compressed (automatically uncompressed on access)
d= not backed up by dump command
i = immutable (file cannot be modified in any way)
s = secure deletion (file zeroed out upon deletion)
S = synchronous updates (files synced to disk when modified)
u = undeletable
Options:

• chattr -R Recursive
  

chfn
Change finger information such as full name, office location, work/home phone#

chgrp [group] [file/directory]
Changes group ownership of files
Options:

• chgrp -R Recursive

chkconfig [service]
View and change service runlevel information
Options:

• chkconfig --list Lists all services and their configuration for each runlevel
• chkconfig --list [service] Lists only the specified service
  
• chkconfig --level 35 [service] on Turns on specified service for runlevels 3 and 5
• chkconfig --del [service] Disables service on all runlevels
• chkconfig --add [service] Enables service on common runlevels
  

chmod [file] or [directory]
Change access mode. Changes file access permissions, default assumes all user types (a)
0 = none
1 = execute
2 = write
3 = write and execute
4 = read
5 = read and execute
6 = read and write
7 = read, write, and execute
Options:

• chmod +rw-x [file] Adds read, write and removes execute permissions to file
  
• chmod ugo+r [file] Adds read permission to user, group, and others (variation: ug+r,o+r)
• chmod u=rwx,g=x,o=r [file] Sets permissions explicitly
  
• chmod 777 [file] Adds read, write, and execute permission to user, group, and others
• chmod u+s [file] Enables the setuid bit
  
• chmod -R Alter permissions recursively
• chmod 6777 [file] Enables the setuid (4) and setgid (2) bits (and permissions 777)
  

chown [owner] [file/directory]
Changes owner of files. Can also be used as "chown [owner:group or owner.group] [file]" to change both owner and group
Options:

• chown -R Recursive
• chown -v Verbose

chpasswd
Changes user passwords in batch. Format: username:password

chsh
Changes your login shell
Options:

• chsh -s [shell - i.e. /bin/bash] Specify shell you want to change to

chvt #
Changes to virtual terminal specified

clear
Clears the screen and puts the prompt in the upper-left hand corner (like the DOS "cls" command)

cmp [file1] [file2]
Compares two files and notifies if differences are found

cp [source file] [destination file/destination directory]
Copies files
Options:

• cp -i Interactive, prompts before overwrite
  
• cp -R Copy recursively
• cp -p Preserves original mode, ownership, & timestamp
• cp -v Verbose
• cp -u Update, only copy source file when it's newer than destination file
• cp -f Force, does not prompt for overwrite confirmation
  

crontab
Crontab management
Options:

• crontab -u [user] Specifies which user's crontab to use
  
• crontab -l Lists crontab contents
  
• crontab -r Removes crontab
• crontab -e Edits current user's crontab
  

cut [file]
Displays specified fields/columns of a file. The default delimiter is a tab
Options:

• cut -d[character] Specify field delimiter as [character]
  
• cut -f# Specify which field to display
• cut -f1,3 Only display fields 1 and 3 
• cut -c# Display the characters in specified column (ranges may also be used such as 11-13)
  

date
Displays the current date and time
Options:

• date -u Displays the time in Greenwich mean time
• date +%H Displays the current hour
• date +%a Displays the current day of the week

df
Displays system's disk space usage
Options:

• df -i List inode information
  
• df -h Display sizes in human readable format (typically aliased to df)
• df -T Displays filesystem types
  

Filesystem            Size  Used Avail Use% Mounted on
/dev/hda6             981M  380M  551M  41% /
/dev/hda1              47M   12M   33M  26% /boot
/dev/hda9             9.7G  9.2G  450M  96% /home
/dev/hda7             1.5G   33M  1.4G   3% /tmp
/dev/hda10             21G   18G  1.8G  92% /usr
/dev/hda8             2.9G  556M  2.2G  20% /var

diff [file1] [file2]
Displays differences between files line-by-line
Options:

• diff -u Output in unified context
  

dmesg
Displays kernel boot messages pertaining to hardware

dpkg (Debian's packaging system)
dpkg-reconfigure - change settings of an existing package
dselect - text based menu package management
alien - rpm2deb and deb2rpm conversions
Options:

• dpkg -L [package] Lists files installed by specified package
  

du
Displays a summary of disk usage for each file and a total usage value, lists recursively from current location
Options:

• du -h Display sizes in human readable format (typically aliased to du)
• du -s Summarizes, does not display directory contents
  
• du -c Displays grand total
  

dump
Filesystem backup utility
Options:

• dump -f [file] Saves backup to file, can be a special file like /dev/st0
  
• dump -[0-9] Specifies backup level. 0 = full backup, 1 = differential backup
• dump -u Updates file /var/lib/dumpdates
  

echo [content]
Used to echo a string to the screen. Using "echo *" displays all the files in current directory

eject [mount point or device]
Ejects removable media. If no mount point or device is specified then cdrom is assumed

env
Displays environment variables

exec [command]
Takes over current shell process and executes specified command. Closes out once finished.

exit
Exit current shell. If currently in login shell then exit will log you out of the session completely

expand [file]  <----fix this
Displays specified fields/columns of a file. The default delimiter is a tab.
Options:

• cut -d[character] Specify field delimiter as [character]
  
• cut -f# Specify which field to display
  

fdisk [drive device] 
Used to alter disk partitions and display partition info
Options:

• fdisk -l Lists the partition table (1 block = 1Kb)
  Disk /dev/hda: 40.0 GB, 40007761920 bytes
  255 heads, 63 sectors/track, 4864 cylinders
  Units = cylinders of 16065 * 512 = 8225280 bytes
  
   Device Boot      Start         End      Blocks   Id  System
  /dev/hda1   *           1           6       48163+  83  Linux
  /dev/hda2               7        4864    39021885    5  Extended
  /dev/hda5               7         133     1020096   82  Linux swap / Solaris
  /dev/hda6             134         260     1020096   83  Linux
  /dev/hda7             261         451     1534176   83  Linux
  /dev/hda8             452         833     3068383+  83  Linux
  /dev/hda9             834        2107    10233373+  83  Linux
  /dev/hda10           2108        4864    22145571   83  Linux
  

Useful commands (within fdisk):
d   delete a partition
l    list known partition types
n   add a new partition
p   print the partition table
t    change a partitions system id (filesystem type)
q   quit without saving changes
v   verify the partition table
w  write table to disk and exit

Command (m for help): p

Disk /dev/sda: 54.5 GB, 54596272128 bytes
255 heads, 63 sectors/track, 6637 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1           4       32098+  de  Dell Utility
/dev/sda2               5        6637    53279572+   5  Extended
/dev/sda5               5         258     2040223+  82  Linux swap / Solaris
/dev/sda6             259         264       48163+  83  Linux
/dev/sda7             265         391     1020096   83  Linux
/dev/sda8             392        1028     5116671   83  Linux
/dev/sda9            1029        4852    30716248+  83  Linux
/dev/sda10           4853        5043     1534176   83  Linux
/dev/sda11           5044        6637    12803773+  83  Linux

Command (m for help): l

 0  Empty                  1e  Hidden W95 FAT1    80  Old Minix                  be  Solaris boot
 1  FAT12                   24  NEC DOS                 81  Minix / old Lin           bf  Solaris
 2  XENIX root           39  Plan 9                      82  Linux swap / So       c1  DRDOS/sec (FAT-
 3  XENIX usr             3c  PartitionMagic          83  Linux                        c4  DRDOS/sec (FAT-
 4  FAT16 <32M         40  Venix 80286            84  OS/2 hidden C:        c6  DRDOS/sec (FAT-
 5  Extended              41  PPC PReP Boot        85  Linux extended       c7  Syrinx
 6  FAT16                   42  SFS                          86  NTFS volume set     da  Non-FS data
 7  HPFS/NTFS            4d  QNX4.x                    87  NTFS volume set     db  CP/M / CTOS / .
 8  AIX                        4e  QNX4.x 2nd part     88  Linux plaintext        de  Dell Utility
 9  AIX bootable         4f  QNX4.x 3rd part       8e  Linux LVM                df  BootIt
 a  OS/2 Boot Manag  50  OnTrack DM             93  Amoeba                  e1  DOS access
 b  W95 FAT32            51  OnTrack DM6 Aux    94  Amoeba BBT           e3  DOS R/O
 c  W95 FAT32 (LBA)   52  CP/M                        9f  BSD/OS                   e4  SpeedStor
 e  W95 FAT16 (LBA)   53  OnTrack DM6 Aux    a0  IBM Thinkpad hi     eb  BeOS fs
 f  W95 Ext'd (LBA)      54  OnTrackDM6            a5  FreeBSD                ee  EFI GPT
10  OPUS                     55  EZ-Drive                  a6  OpenBSD              ef  EFI (FAT-12/16/
11  Hidden FAT12        56  Golden Bow             a7  NeXTSTEP             f0  Linux/PA-RISC b
12  Compaq diagnost  5c  Priam Edisk              a8  Darwin UFS           f1  SpeedStor
14  Hidden FAT16 <3   61  SpeedStor               a9  NetBSD                 f4  SpeedStor
16  Hidden FAT16        63  GNU HURD or Sys     ab  Darwin boot         f2  DOS secondary
17  Hidden HPFS/NTF   64  Novell Netware        b7  BSDI fs                 fd  Linux raid auto
18  AST SmartSleep     65  Novell Netware        b8  BSDI swap            fe  LANstep
1b  Hidden W95 FAT3  70  DiskSecure Mult       bb  Boot Wizard hid    ff  BBT
1c  Hidden W95 FAT3   75  PC/IX

fg [job#]
Bring background job back to foreground. If no job is specified then the current job is brought to the foreground

file [filename]
Attempts to determine filetype of specified file

find [optional location]
Searches for files. Operators that can be used between expressions: ! = not, -a = and, -o = or
Options:

• find -mtime # Find files modified in last # days
  
• find -mmin # Find files modified in last # minutes
  
• find -atime # Find files accessed in last # days
  
• find -amin # Find files accessed in last # minutes
  
• find -user [username] Find files owned by specified user
• find -group [groupname] Find files owned by specified group
• find -type [filetype] Find files of specific filetype (d = directory, f = file, l = symbolic link)
  
• find -name "[search criteria/pattern]" Find files matching criteria
  
• find -iname "[search criteria/pattern]" Same as -name, but search is case insensitive
  
• find -exec [command] {} \; Execute command on all files located with find
• find -L Follow symbolic links
• find -empty Displays empty files
• find -size +1G Displays files larger than 1GB. b = bytes, k = kilobytes, M = megabytes, G = gigabytes
• find -size +1M -size -10M Displays files larger than 1MB but smaller than 10MB
• find -ls Displays files found in an "ls -l" similar format
• find -perm 0755 Displays files that have specified permissions

finger [user]
Displays user information
Login: resinblade                              Name: Eric
Directory: /home/resinblade             Shell: /bin/bash
On since Wed Aug 25 10:25 (EDT) on tty7 from :0
    7 hours 19 minutes idle
On since Wed Aug 25 10:27 (EDT) on pts/0 from :0.0
   20 minutes 54 seconds idle
On since Wed Aug 25 13:23 (EDT) on pts/1 from :0.0
On since Wed Aug 25 13:24 (EDT) on pts/2 from :0.0
   19 minutes 3 seconds idle
No mail.
No Plan.

free
Displays system memory usage
Options:

• free -m Displays values in megabytes instead of default kilobytes
  

grep [pattern] [optional file]
Display results that match specified pattern
Options:

• grep -i Ignore case
• grep -h Hide filenames when searching multiple files
• grep -l List only matching filenames
• grep -n List associated line number
  
• grep -v Displays results that do not match specified pattern (inverse/not)
• grep -w Matches only whole words
• grep -r Recursive search
• grep -c Displays total count of matches found next to corresponding filenames
  

groupadd [group]
Creates specified group
Options:

• groupadd -g [GID] Specifies GID
  

groupdel [group]
Removes specified group

groupmod [group]
Alters group settings for specified group
Options:

• groupmod -n [new groupname] Changes group name
  

groups
Lists groups that current user is a member of

grpck
Checks the integrity of the /etc/group files

gzip/gunzip [file/directory]
Compress files
Options:

• gzip -v Verbose
  
• gzip -r Recursive
  

halt
Shuts down the system

head [file]
Display first 10 lines of specified file
Options:

• head -n # Change amount of lines displayed to #
  

hdparm [drive device]
K <---Fix this
/dev/sda:
 IO_support    =  0 (default)
 readonly      =  0 (off)    
 readahead     = 256 (on)    
 geometry      = 4863/255/63, sectors = 78125000, start = 0

sectors * 512 = size of drive

Options:

• hdparm -I Displays detailed information about drive
  /dev/sda:
  ATA device, with non-removable media
          Model Number:       WDC WD400BB-75JHC0                     
          Serial Number:      WD-WMAMC7021156                        
          Firmware Revision:  06.01C06                               
  Standards:                                                         
          Supported: 6 5 4                                           
          Likely used: 8                                             
  Configuration:                                                     
          Logical         max     current                            
          cylinders       16383   16383                              
          heads           16      16                                 
          sectors/track   63      63                                 
          --                                                         
          CHS current addressable sectors:   16514064                
          LBA    user addressable sectors:   78125000                
          device size with M = 1024*1024:       38146 MBytes         
          device size with M = 1000*1000:       40000 MBytes (40 GB) 
  Capabilities:                                                      
          LBA, IORDY(can be disabled)                                
          Standby timer values: spec'd by Standard, with device specific minimum
          R/W multiple sector transfer: Max = 16  Current = 16                 
          Recommended acoustic management value: 128, current value: 254       
          DMA: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 *udma5          
               Cycle time: min=120ns recommended=120ns                         
          PIO: pio0 pio1 pio2 pio3 pio4                                        
               Cycle time: no flow control=120ns  IORDY flow control=120ns     
  Commands/features:
          Enabled Supported:
             *    SMART feature set
                  Security Mode feature set
             *    Power Management feature set
             *    Write cache
             *    Look-ahead
             *    Host Protected Area feature set
             *    WRITE_BUFFER command
             *    READ_BUFFER command
             *    DOWNLOAD_MICROCODE
                  SET_MAX security extension
             *    Automatic Acoustic Management feature set
             *    Device Configuration Overlay feature set
             *    Mandatory FLUSH_CACHE
             *    SMART error logging
             *    SMART self-test
             *    SMART Command Transport (SCT) feature set
             *    SCT Long Sector Access (AC1)
             *    SCT LBA Segment Access (AC2)
             *    SCT Error Recovery Control (AC3)
             *    SCT Features Control (AC4)
             *    SCT Data Tables (AC5)
  Security:
          Master password revision code = 65534
                  supported
          not     enabled
          not     locked
          not     frozen
          not     expired: security count
          not     supported: enhanced erase
  HW reset results:
          CBLID- above Vih
          Device num = 0 determined by CSEL
  Checksum: correct
  
  
• hdparm -t Performs device read benchmark
  /dev/sda:
   Timing buffered disk reads:  122 MB in  3.02 seconds =  40.34 MB/sec
  
• hdparm -T Performs cache read benchmark
  /dev/sda:
   Timing cached reads:   210 MB in  2.02 seconds = 104.15 MB/sec

history
Lists entire history of command line input
Stored by default in ~/.bash_history or possibly another file specified in the variable HISTFILE.
The size of the history file depends on these two variables - HISTFILESIZE and HISTSIZE.
HISTFILESIZE = max number of lines in history file
HISTSIZE = max number of commands remembered in history file.
Options:

• history -c Clears history
  

hostname
Displays system hostname
Options:

• hostname -f Display the FQDN
  

iastlog
Displays last login time for all users. Pulls data from /var/log/lastlog
Options:

• lastlog -u [user] Only lists specified user
  

logger
Logs input to syslog

id
Displays real and effective UIDs and GIDs of current user

ifconfig
Displays status of network interfaces. "ifconfig eth0 | grep inet", displays just the line listing the IP address
Options:

• ifconfig eth0 [ip address] Set IP address
  
• ifconfig eth0 netmask [subnet mask] Set subnet mask
• ifconfig eth0 down/up Enable/disable interface (also ifdown/ifup)
• ifconfig eth0 hw ether [MAC address (colon seperators)] Change MAC address
• ifconfig eth0:0 [ip address] Set first IP alias
• ifconfig -a Lists all adapters whether up or down
  

[program name/command]
Displays info documentation for specified topic. CTRL-H will list the basic commands for info
q = quits info
TAB = cycle through nodes (links) on page
n = next node
p = previous node
ENTER = goto selected node
u = move up in hierarchy

init [runlevel]
Changes system to specified runlevel

jobs
Lists jobs running in the background

kbdconfig (deprecated, was used in Red Hat)
Used to change keyboard mapping. Must be root to run. Located in /usr/sbin

kill [PID]
Terminates an open process. Default kill signal is TERM (15).
Kill signals:
1 - SIGHUP, used with daemons to issue a restart
9 - SIGKILL, forcibily kills a process
15 - SIGTERM, default kill method, asks a program to stop
-SIGSTOP, suspends a process
-SIGCONT, resumes a process
Options:

• kill -l Display a list of signal types
  
• kill -[signal#] Kills process with specified signal type
  

killall [process name]
Kills all instances of named process. Default kill signal is TERM (15).
Options:

• killall -i Interactive, prompts before killing each process
  
• killall -[signal#] Kills process with specified signal type
• killall -v Verbose
  

last
Displays last users to login

ldd [executable path]
Display shared library dependencies for specifed program

less [text file]
Displays contents of a text file and allows scrolling throughout it. A text viewer that in my opinion is superior to "more". Running less as "less +F" will run it in follow mode (useful for lgo files)
up, down arrow keys = scrolling
h = display help
/string = search forward for specified string
?string = search backward for specified string
n = repeat last search
#G = go to specified line number
page down, spacebar = go forward one screen at a time
page up, b = go back one screen at a time
q = quit

ln [file/location] [new link]
Creates a hardlink by default (new name for the same file)
Options:

• ln -s Creates a symbolic link (similar to a shortcut)
  

locate [search criteria]
Searches for files based on criteria. "updatedb" (requires root) must be ran for up-to-date results

look [string]
This command looks up words in a dictionary, useful for checking spelling. Entering "e" as the character would show all words in the dictionary that begin with the letter "e", and so on.

logout
Used to terminate login shells only

lpq
Displays printer queue status
Options:

• lpq -a Reports jobs on all printers
  
• lpq -P[printer name] Printer destination

lpr [file] or [file] [file] [file] <----several files at once
Prints file to default printer
Options:

• lpr -#[number] Number of copies, 1-100
  
• lpr -P[printer name] Printer destination
• lpr -m Send email on print job completion
  

lprm [print job ID]
Cancels specified print job. If no print job is specified then the current job on the default printer is canceled.
Options:

• lprm -P[printer name] Printer destination
  

ls or ls [directory]
This command lists a directory's contents much like the DOS "dir" command.
Options:

• ls -a Lists absolutely all files even hidden ones (like DOS "dir /a")
  
• ls -l Long listing (detailed)  (sometimes aliased as ll)
  -rw-r--r-- 1 root root 629 Nov 30 01:02 dhcpd.conf
  permissions, number of links to object, owner, group, time last modified, name
  lrwxrwxrwx  = link,  crw-rw---- = character device, drwxr-xr-x = directory
  brw------- = block device, prw-------, srw-rw-rw-
  
• ls -s Lists files and their sizes rounded in kilobytes
  
• ls -t Sort by modification time. Most recently modified files are listed at top descending down to oldest last modified times
  
• ls ~ Lists contents of the current user's home directory
  
• ls ~[username] Lists contents of the specified user's home directory
  
• ls -h Lists file sizes in a human friendly format such as 30K instead of 30000 bytes
  
• ls -x Lists files in rows rather than columns
  
• ls -r Sorts files in reverse alphabetical order
  
• ls -S Sorts files by file size, largest files first
  
• ls -R Lists files and subdirectories recursively
  
• ls -d Lists directories, but not their contents
  
• ls -i Lists the inode number for each file
  
• ls -F Appends file type symbol to entries (aliased to "ls" in Mandriva Linux)
• ls -1 Lists one file per line in a column format
• ls -X Sorts files in alphabetical order by file extension
  

lsattr [file]
Lists file attributes for specified file

lsof
Lists open files

md5sum [file] 
Computes and verifies MD5 checksums of files
Options:

• md5sum -c file.md5 Check hashes listed in file.md5 against specified files
  

mii-tool [ethernet interface] 
Outdated - replaced by ethtool.  Views and alters media-independent interfaces (ethernet cards)
Must be root to run
eth0: negotiated 100baseTx-FD flow-control, link ok
Options:

• mii-tool -v verbose, detailed information
  eth0: negotiated 100baseTx-FD flow-control, link ok
    product info: vendor 00:50:ef, model 12 rev 0
    basic mode:   autonegotiation enabled
    basic status: autonegotiation complete, link ok
    capabilities: 100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD
    advertising:  100baseTx-FD 100baseTx-HD 10baseT-FD 10baseT-HD flow-control
    link partner: 100baseTx-FD 100baseTx-H
  
  
• mii-tool -w Watch interface for changes in link status
• mii-tool -R Resets interface to default configuration
• mii-tool -F [speed/duplex i.e. 100baseTX-HD] Forces a specified speed and duplex
  
• mii-tool -A [speed i.e. 10baseT] Advertises support for specified speed (and/or duplex)
  

• mdkir -p /[directory]/[directory]/[directory]... create specified parent directories (if necessary)

• mount -t Specifies filesystem type i.e. vfat, ext3
• mount -o rw Mounts filesystem as read-write
• mount -o remount,ro Remounts filesystem as read-only
• mount -a Mounts all filesystems listed in /etc/fstab
  

mv [source file] [destination file/desination directory]
Renames (moves) a file.
Options:

• mv -i Interactive, prompt before overwrite
• mv -v Verbose
• mv -f Force, does not prompt for overwrite confirmation
  

netconfig (deprecated, was used in Red Hat)
Used to change TCP/IP network settings. Must be root to run. Located in /usr/sbin

netstat
Displays list of open sockets
Options:

• netstat -a Displays all sockets (listening and non-listening)
  
• netstat -n Displays numerical addresses instead of hostnames
• netstat -p Displays program names associated with sockets
• netstat -t Display TCP traffic only
  
• netstat -u Display UDP traffic only
• 
  
• netstat -r Displays routing table
  

• newgrp - Reinitializes login with group specified
  

nl [file]
Numbers lines of specified file

nslookup [domain name]
Queries DNS servers and returns IP information

od [file]
Dumps a file in octal format
Options:

• od -c Displays ASCII characters
  
• od -x Displays in hex format
  

• paste -s Serializes each file. Contents are on a single line only
  
• paste -d[character] Specify delimiter as [character]
  

restore
Restores files from dump backups
Options:

• restore -i Interactive restore. Allows contents of dump to be browsed and files to be chosen for restore
  
• restore -f [file] Restore backup from specified file
  
• restore -C Compares restored files to dump file
  
• restore -v Verbose
• restore -r Complete restore
  

• rmdir -p [directory]/[directory] removes specified directory structure
  

route
Displays routing table
Options:

• route add default gw [IP address] Sets default gateway
• route -n Displays routing table without DNS lookup

• rpm -i [package file] Installs specified package file onto the system
  
• rpm -q [package name] Queries installed packages to check to see if specified package is currently installed
• rpm -qa [package name] Query all installed packages
• rpm -qi [package name] Query and display package info including name, version, and description
• rpm -ql [package name] Query and display list of files installed by specified package
• rpm -qlp [rpm file] Query and display list of files included in specified package file
  
• rpm -qf [file path] Query and display which package owns specified file
• rpm -U [package file] Upgrades specified package to newer version supplied in package file
  
• rpm -v Verbose
• rpm -V [package name] Verifies integrity of installed package
• rpm -e [package name] Erase, uninstalls specifed package
• rpm -h Displays a hash marked progress bar
• rpm -F [package file] Freshen, upgrades specifed package only if a previous version is currently installed

runlevel
Displays previous and current runlevels

sed
Stream editor, used to manipulate text.
Options:

• sed 's/String1/String2/' All instances of "string1" are replaced by "string2"
• sed - D
  

service [service name] start/restart/stop/status
Reports or manipulates service state. Requires superuser access.
Options:

• service --status-all Displays status of all services
  

set
Displays the list of environment variables

shutdown -[options] [time (in minutes) or now] [optional warning message]
Shutdowns the system in various ways. Requires superuser access.
Options:

• shutdown -k Don't shutdown just send warning message
• shutdown -F Force fsck on reboot
• shutdown -f Skip fsck on reboot (fast boot)
  
• shutdown -h Halt after shutdown (complete shutdown or powerdown)
• shutdown -r Reboot after shutting down
• shutdown -c Cancel shutdown
• shutdown -t [seconds] Waits specified amount of seconds before shutting down
  

• sort -r Sorts in descending order (reverse order)
• sort -n Sorts numerically

stat [file]
C
File: `writing.txt'
Size: 414             Blocks: 4          IO Block: 4096   regular file
Device: 309h/777d       Inode: 808403      Links: 1
Access: (0664/-rw-rw-r--)  Uid: (  500/resinblade)   Gid: (  500/resinblade)
Access: 2007-03-29 21:10:08.000000000 -0400
Modify: 2007-03-20 20:46:23.000000000 -0400
Change: 2007-05-04 08:22:01.000000000 -0400

File: "me_djy.avi"
ID: 0        Namelen: 255     Type: ext2/ext3
Block size: 1024       Fundamental block size: 1024
Blocks: Total: 10070256   Free: 175239     Available: 175239
Inodes: Total: 1280000    Free: 1228093

Options:

• chmod +rw-x [file] Adds read, write and removes execute permissions to file
  
• chmod ugo+r [file] Adds read permission to user, group, and owner
  

strings [file]
Displays any ASCII characters available in specified file.
Options:

• strings -n # Display character sequences that are length of #. Default is 4.
  

su [optional username]
Substitute user that's currently logged with the user specified. If no user is specified then it's assumed to be root
Options:

• - Process login for user
  
• su -c [command] Pass single command and do not switch users
  

sudo/sudo echo

suspend
Sends current job to the background

swapoff [device] 
Disables device for swapping
Options:

• swapoff -a Disables swap for all swap devices
  

swapon [device] 
Enables device for swapping
Options:

• swapon -a Enables swap for all swap devices
• swapon -s Displays summary of swap usage
  

tac [file]
Displays file in reverse, opposite of cat

talk [user]
Begins talk session with specified user

tail [file]
Display last 10 lines of specified file
Options:

• tail -n # Change amount of lines displayed to #
• tail -f Follow (display) new changes to specified file(s)
  

tar [archive]
Tape archiver program. Used for combining files into a single archive or extracting files from an archive. Typical operation is similar to - tar xvf <file name>
Options:

• x Extract files from archive
  
• v Verbosely lists files being processed
• c Create a new archive
• t List the contents of an archive
  
• f Use an archive file
• z Filter archive through gzip
• j Filter archive through bzip2
• r Add files to existing archive
• k Keeps old files, doesn't overwrite existing files during an extract
• m Changes modificaton time of files during an extract to time of extraction
  

• k Kill a process, will ask for a PID to kill, then for signal type - default 15
  
• M Sort processes by memory usage
• P Sorts processes by CPU usage (default)
  
• u Sort processes by given username
• i Idle toggle, toggles between all processes and those with that are actively running
  
• h Help
• q Quit

• find -mtime # find files modified in last # days
  
• find -mmin # find files modified in last # minutes
  
• find -atime # find files accessed in last # days
  
• find -amin # find files accessed in last # minutes

tty
Display what terminal the current user is connected to

ulimit
Lists and changes system limitations
Options:

• ulimit -a Lists all current limits
  

umask [###]  <---umask value
Displays default umask setting is typically 022. To find the actual file permission subtract the umask value from 666 for files and from 777 for directories. Umask 022 will result in files being 644 and directories as 755
Options:

• umask -S Displays the umask symbolically
  u=rwx,g=rx,o=rx
  

umount [path]
Unmount filesystem mounted at specified path

unalias [alias]
Remove specified alias

uname
Displays system information such as kernel version, processor type, hostname, etc. No options specified defaults to -s
Options:

• uname -a Displays all information
  Linux mandriva.dbccwire.net 2.6.12-12mdksmp #1 SMP Fri Sep 9 17:43:23 CEST 2005 i686 Pentium III (Coppermine) unknown GNU/Linux
• uname -p Displays processor type
• uname -s Displays kernel name
• uname -r Displays kernel release
  

• uniq -c Display count of occurrences
  
• uniq -d Only display duplicate lines
  

• urpmi --force Assumes yes to all questions
• urpmi --auto-update Updates install media then proceeds to install all available updates
• urpmi --clean Removes all packages in /var/cache/urpmi/rpms
  

• useradd -m Creates home directory
• useradd -m -k [directory] Creates home directory and copies user configuration from specified directory
  
• useradd -c [full name] Full name (comments)
  
• useradd -s [shell] Specifies login shell (can be specified as /bin/false for users that do not login)
  
• useradd -g [groupname or GID] Sets initial login group
  
• useradd -u [UID] Sets UID
• useradd -d [homedir path] Specifies a non-default homedir location
• useradd -e [YYYY-MM-DD] Sets expiration date
• useradd -G [group1,group2] Adds user to supplementary groups 1 and 2
• useradd -D Displays default useradd values, with options can be used to change the values
  

• userdel -r Deletes home directory
  

• usermod -l [old username] [new username] Changes username to new speficied name. Home directory has to be renamed manually
  
• usermod -c [full name] Changes full name (comments)
• usermod -g [group] Changes initial login group
• usermod -G [group1,group2,group3] Changes user's group membership to only the groups specified
• usermod -a -G [group1,group2,group3] Adds user to groups specified (will not remove group membership if a group is not specified like -G)
• usermod -s [shell path] Changes default shell
  

• wc -w Word count
• wc -l Newline count
• wc -m Character count
• wc -c Byte count

who
Displays who is currently logged into the system
Options:

• who -q Gives a count of total number of users logged in and lists their name
• who -H Displays the who content with column headings
• who -u Adds idle time to who content (used to be -i)