Showing posts with label Linux. Show all posts
Showing posts with label Linux. Show all posts

Thursday, March 29, 2012

An A-Z Index of the Bash command line for Linux

An A-Z Index of the Bash command line for Linux
a
alias Create an alias
apropos Search Help manual pages (man -k)
apt-get Search for and install software packages (Debian)
aspell Spell Checker
awk Find and Replace text, database sort/validate/index
b
bash GNU Bourne-Again SHell
bc Arbitrary precision calculator language
bg Send to background
break Exit from a loop
builtin Run a shell builtin
bzip2 Compress or decompress named file(s)
c
cal Display a calendar
case Conditionally perform a command
cat Display the contents of a file
cd Change Directory
cfdisk Partition table manipulator for Linux
chgrp Change group ownership
chmod Change access permissions
chown Change file owner and group
chroot Run a command with a different root directory
chkconfig System services (runlevel)
cksum Print CRC checksum and byte counts
clear Clear terminal screen
cmp Compare two files
comm Compare two sorted files line by line
command Run a command - ignoring shell functions
continue Resume the next iteration of a loop
cp Copy one or more files to another location
cron Daemon to execute scheduled commands
crontab Schedule a command to run at a later time
csplit Split a file into context-determined pieces
cut Divide a file into several parts
d
date Display or change the date & time
dc Desk Calculator
dd Convert and copy a file, write disk headers, boot records
ddrescue Data recovery tool
declare Declare variables and give them attributes
df Display free disk space
diff Display the differences between two files
diff3 Show differences among three files
dig DNS lookup
dir Briefly list directory contents
dircolors Colour setup for `ls'
dirname Convert a full pathname to just a path
dirs Display list of remembered directories
dmesg Print kernel & driver messages
du Estimate file space usage
e
echo Display message on screen
egrep Search file(s) for lines that match an extended expression
eject Eject removable media
enable Enable and disable builtin shell commands
env Environment variables
ethtool Ethernet card settings
eval Evaluate several commands/arguments
exec Execute a command
exit Exit the shell
expect Automate arbitrary applications accessed over a terminal
expand Convert tabs to spaces
export Set an environment variable
expr Evaluate expressions
f
false Do nothing, unsuccessfully
fdformat Low-level format a floppy disk
fdisk Partition table manipulator for Linux
fg Send job to foreground
fgrep Search file(s) for lines that match a fixed string
file Determine file type
find Search for files that meet a desired criteria
fmt Reformat paragraph text
fold Wrap text to fit a specified width.
for Expand words, and execute commands
format Format disks or tapes
free Display memory usage
fsck File system consistency check and repair
ftp File Transfer Protocol
function Define Function Macros
fuser Identify/kill the process that is accessing a file
g
gawk Find and Replace text within file(s)
getopts Parse positional parameters
grep Search file(s) for lines that match a given pattern
groups Print group names a user is in
gzip Compress or decompress named file(s)
h
hash Remember the full pathname of a name argument
head Output the first part of file(s)
history Command History
hostname Print or set system name
i
id Print user and group id's
if Conditionally perform a command
ifconfig Configure a network interface
ifdown Stop a network interface
ifup Start a network interface up
import Capture an X server screen and save the image to file
install Copy files and set attributes
j
join Join lines on a common field
k
kill Stop a process from running
killall Kill processes by name
l
less Display output one screen at a time
let Perform arithmetic on shell variables
ln Make links between files
local Create variables
locate Find files
logname Print current login name
logout Exit a login shell
look Display lines beginning with a given string
lpc Line printer control program
lpr Off line print
lprint Print a file
lprintd Abort a print job
lprintq List the print queue
lprm Remove jobs from the print queue
ls List information about file(s)
lsof List open files
m
make Recompile a group of programs
man Help manual
mkdir Create new folder(s)
mkfifo Make FIFOs (named pipes)
mkisofs Create an hybrid ISO9660/JOLIET/HFS filesystem
mknod Make block or character special files
more Display output one screen at a time
mount Mount a file system
mtools Manipulate MS-DOS files
mv Move or rename files or directories
mmv Mass Move and rename (files)
n
netstat Networking information
nice Set the priority of a command or job
nl Number lines and write files
nohup Run a command immune to hangups
nslookup Query Internet name servers interactively
o
open Open a file in its default application
op Operator access
p
passwd Modify a user password
paste Merge lines of files
pathchk Check file name portability
ping Test a network connection
pkill Stop processes from running
popd Restore the previous value of the current directory
pr Prepare files for printing
printcap Printer capability database
printenv Print environment variables
printf Format and print data
ps Process status
pushd Save and then change the current directory
pwd Print Working Directory
q
quota Display disk usage and limits
quotacheck Scan a file system for disk usage
quotactl Set disk quotas
r
ram ram disk device
rcp Copy files between two machines
read read a line from standard input
readonly Mark variables/functions as readonly
reboot Reboot the system
renice Alter priority of running processes
remsync Synchronize remote files via email
return Exit a shell function
rev Reverse lines of a file
rm Remove files
rmdir Remove folder(s)
rsync Remote file copy (Synchronize file trees)
s
screen Multiplex terminal, run remote shells via ssh
scp Secure copy (remote file copy)
sdiff Merge two files interactively
sed Stream Editor
select Accept keyboard input
seq Print numeric sequences
set Manipulate shell variables and functions
sftp Secure File Transfer Program
shift Shift positional parameters
shopt Shell Options
shutdown Shutdown or restart linux
sleep Delay for a specified time
slocate Find files
sort Sort text files
source Run commands from a file `.'
split Split a file into fixed-size pieces
ssh Secure Shell client (remote login program)
strace Trace system calls and signals
su Substitute user identity
sudo Execute a command as another user
sum Print a checksum for a file
symlink Make a new name for a file
sync Synchronize data on disk with memory
t
tail Output the last part of files
tar Tape ARchiver
tee Redirect output to multiple files
test Evaluate a conditional expression
time Measure Program running time
times User and system times
touch Change file timestamps
top List processes running on the system
traceroute Trace Route to Host
trap Run a command when a signal is set(bourne)
tr Translate, squeeze, and/or delete characters
true Do nothing, successfully
tsort Topological sort
tty Print filename of terminal on stdin
type Describe a command
u
ulimit Limit user resources
umask Users file creation mask
umount Unmount a device
unalias Remove an alias
uname Print system information
unexpand Convert spaces to tabs
uniq Uniquify files
units Convert units from one scale to another
unset Remove variable or function names
unshar Unpack shell archive scripts
until Execute commands (until error)
useradd Create new user account
usermod Modify user account
users List users currently logged in
uuencode Encode a binary file
uudecode Decode a file created by uuencode
v
v Verbosely list directory contents (`ls -l -b')
vdir Verbosely list directory contents (`ls -l -b')
vi Text Editor
vmstat Report virtual memory statistics
w
watch Execute/display a program periodically
wc Print byte, word, and line counts
whereis Report all known instances of a command
which Locate a program file in the user's path.
while Execute commands
who Print all usernames currently logged in
whoami Print the current user id and name (`id -un')
Wget Retrieve web pages or files via HTTP, HTTPS or FTP
write Send a message to another user
x
xargs Execute utility, passing constructed argument list(s)
yes Print a string until interrupted
. Run a command script in the current shell
### Comment / Remark
SS64 Discussion forum
Bash commands for OS X
Links to other Sites, full list of man pages, books etc...

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Monday, October 31, 2011

How to disable ICMP echo responses in Linux

Many malicious attacks begin with a ping scan. Disabling ICMP echo requests prevents your system’s discovery with a ping.

Disable ICMP echo responses temporarily

You can temporarily disable the ICMP using the following method but this setting will be erased after the reboot.

root@lifelinux:~# echo 1 >  /proc/sys/net/ipv4/icmp_echo_ignore_all

Also, to enable the ICMP echo responses back, type the following command:

root@lifelinux:~# echo 0 >  /proc/sys/net/ipv4/icmp_echo_ignore_all

Disable ICMP echo responses permanently

You can permanently disable the ICMP echo reponses using the following method:
Edit the sysctl.conf file:

root@lifelinux:~# vi /etc/sysctl.conf

And add the following line:

net.ipv4.icmp_echo_ignore_all = 1

After that, execute sysctl -p to enforce this setting immediately:

root@lifelinux:~# sysctl -p

The above command loads the sysctl settings from the sysctl.conf.

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Sunday, August 7, 2011

Enabling And Disabling Services During Start Up In GNU/Linux

In any Linux distribution, some services are enabled to start at boot up by default. For example, on my machine, I have pcmcia, cron daemon, postfix mail transport agent ... just to name a few, which start during boot up. Usually, it is prudent to disable all services that are not needed as they are potential security risks and also they unnecessarily waste hardware resources. For example, my machine does not have any pcmcia cards so I can safely disable it. Same is the case with postfix which is also not used.

So how do you disable these services so that they are not started at boot time?

The answer to that depends on the type of Linux distribution you are using. True, many Linux distributions including Ubuntu bundle with them a GUI front end to accomplish the task which makes it easier to enable and disable the system services. But there is no standard GUI utility common across all Linux distributions. And this makes it worth while to learn how to enable and disable the services via the command line.

But one thing is common for all Linux distributions which is that all the start-up scripts are stored in the '/etc/init.d/' directory. So if you want to say, enable apache webserver in different run levels, then you should have a script related to the apache webserver in the /etc/init.d/ directory. It is usually created at the time of installing the software. And in my machine (which runs Ubuntu), it is named apache2. Where as in Red Hat, it is named httpd. Usually, the script will have the same name as the process or daemon.

Here I will explain different ways of enabling and disabling the system services.
1) Red Hat Method

Red Hat and Red Hat based Linux distributions make use of the script called chkconfig to enable and disable the system services running in Linux.

For example, to enable the apache webserver to start in certain run levels, you use the chkconfig script to enable it in the desired run levels as follows:

# chkconfig httpd --add
# chkconfig httpd on --level 2,3,5
This will enable the apache webserver to automatically start in the run levels 2, 3 and 5. You can check this by running the command:
# chkconfig --list httpd
One can also disable the service by using the off flag as shown below:
# chkconfig httpd off
# chkconfig httpd --del
Red Hat also has a useful script called service which can be used to start or stop any service. Taking the previous example, to start apache webserver, you execute the command:
# service httpd start
and to stop the service...
# service httpd stop
The options being start, stop and restart which are self explanatory.
2) Debian Method

Debian Linux has its own script to enable and disable services across runlevels. It is called update-rc.d. Going by the above example, you can enable apache webserver as follows:

# update-rc.d apache2 defaults

... this will enable the apache webserver to start in the default run levels of 2,3,4 and 5. Of course, you can do it explicitly by giving the run levels instead of the "defaults" keyword as follows:

# update-rc.d apache2 start 20 2 3 4 5 . stop 80 0 1 6 .

The above command modifies the sym-links in the respective /etc/rcX.d directories to start or stop the service in the destined runlevels. Here X stands for a value of 0 to 6 depending on the runlevel. One thing to note here is the dot (.) which is used to terminate the set which is important. Also 20 and 80 are the sequence codes which decides in what order of precedence the scripts in the /etc/init.d/ directory should be started or stopped.

And to disable the service in all the run levels, you execute the command:

# update-rc.d -f apache2 remove
Here -f option which stands for force is mandatory.

But if you want to enable the service only in runlevel 5, you do this instead:

# update-rc.d apache2  start 20 5 . stop 80 0 1 2 3 4 6 .
3) Gentoo Method

Gentoo also uses a script to enable or disable services during boot-up. The name of the script is rc-update . Gentoo has three default runlevels. Them being: boot, default and nonetwork. Suppose I want to add the apache webserver to start in the default runlevel, then I run the command:

# rc-update add apache2 default
... and to remove the webserver, it is as simple as :
# rc-update del apache2
To see all the running applications at your runlevel and their status, similar to what is achieved by chkconfig --list, you use the rc-status command.
# rc-status --all
4) The old fashioned way

I remember the first time I started using Linux, there were no such scripts to aid the user in enabling or disabling the services during start-up. You did it the old fashioned way which was creating or deleting symbolic links in the respective /etc/rcX.d/ directories. Here X in rcX.d is a number which stands for the runlevel. There can be two kinds of symbolic links in the /etc/rcX.d/ directories. One starts with the character 'S' followed by a number between 0 and 99 to denote the priority, followed by the name of the service you want to enable. The second kind of symlink has a name which starts with a 'K' followed by a number and then the name of the service you want to disable. So in any runlevel, at any given time, for each service, there should be only one symlink of the 'S' or 'K' variety but not both.

So taking the above example, suppose I want to enable apache webserver in the runlevel 5 but want to disable it in all other runlevels, I do the following:

First to enable the service for run level 5, I move into /etc/rc5.d/ directory and create a symlink to the apache service script residing in the /etc/init.d/ directory as follows:

# cd /etc/rc5.d/
# ln -s /etc/init.d/apache2 S20apache2

This creates a symbolic link in the /etc/rc5.d/ directory which the system interprets as - start (S) the apache service before all the services which have a priority number greater than 20.

If you do a long listing of the directory /etc/rc5.d in your system, you can find a lot of symlinks similar to the one below.

lrwxrwxrwx  1 root root 17 Mar 31 13:02 S20apache2 -> ../init.d/apache2

Now if I start a service, I will want to stop the service while rebooting or while moving to single user mode and so on. So in those run levels I have to create the symlinks starting with character 'K'. So going back to the apache2 service example, if I want to automatically stop the service when the system goes into runlevel 0, 1 or 6, I will have to create the symlinks as follows in the /etc/rc0.d, /etc/rc1.d/, /etc/rc6.d/ directories.

# ln -s /etc/init.d/apache2 K80apache2

One interesting aspect here is the priority. Lower the number, the higher is the priority. So since the starting priority of apache2 is 20 - that is apache starts way ahead of other services during startup, we give it a stopping priority of 80. There is no hard and fast rule for this but usually, you follow the formula as follows:

If you have 'N' as the priority number for starting a service, you use the number (100-N) for the stopping priority number and vice versa.

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Tuesday, June 28, 2011

Basic vi Commands

Linux
i or insert to insert text
ii ir insert insert to replace (overwrite)
arrow keys to navigate
esc :q! to exit with out changes
esc :wq to save and exit
my fave
esc shift^ZZ to save and exit.


*BSD
same as above but no arrow keys and sometimes no insert i(only)
esc takes you to command mode and you can navigate
.with keys
x =delete
h,j,k,l = arrows
etc...
just the very basics
Almost forgot that *BSD has an editor ee I like alot when you're done editing
esc and you get a little menu

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Thursday, May 5, 2011

linux command line reference for common operations

 
 
This is a linux command line reference for common operations.
Examples marked with • are valid/safe to paste without modification into a terminal, so
you may want to keep a terminal window open while reading this so you can cut & paste.
All these commands have been tested both on Fedora and Ubuntu.
 

 
Command Description
apropos whatis Show commands pertinent to string. See also threadsafe
man -t ascii | ps2pdf - > ascii.pdf make a pdf of a manual page
  which command Show full path name of command
  time command See how long a command takes
time cat Start stopwatch. Ctrl-d to stop. See also sw
dir navigation
cd - Go to previous directory
cd Go to $HOME directory
  (cd dir && command) Go to dir, execute command and return to current dir
pushd . Put current dir on stack so you can popd back to it
alias l='ls -l --color=auto' quick dir listing
ls -lrt List files by date. See also newest and find_mm_yyyy
ls /usr/bin | pr -T9 -W$COLUMNS Print in 9 columns to width of terminal
  find -name '*.[ch]' | xargs grep -E 'expr' Search 'expr' in this dir and below. See also findrepo
  find -type f -print0 | xargs -r0 grep -F 'example' Search all regular files for 'example' in this dir and below
  find -maxdepth 1 -type f | xargs grep -F 'example' Search all regular files for 'example' in this dir
  find -maxdepth 1 -type d | while read dir; do echo $dir; echo cmd2; done Process each item with multiple commands (in while loop)
find -type f ! -perm -444 Find files not readable by all (useful for web site)
find -type d ! -perm -111 Find dirs not accessible by all (useful for web site)
locate -r 'file[^/]*\.txt' Search cached index for names. This re is like glob *file*.txt
look reference Quickly search (sorted) dictionary for prefix
grep --color reference /usr/share/dict/words Highlight occurances of regular expression in dictionary
archives and compression
  gpg -c file Encrypt file
  gpg file.gpg Decrypt file
  tar -c dir/ | bzip2 > dir.tar.bz2 Make compressed archive of dir/
  bzip2 -dc dir.tar.bz2 | tar -x Extract archive (use gzip instead of bzip2 for tar.gz files)
  tar -c dir/ | gzip | gpg -c | ssh user@remote 'dd of=dir.tar.gz.gpg' Make encrypted archive of dir/ on remote machine
  find dir/ -name '*.txt' | tar -c --files-from=- | bzip2 > dir_txt.tar.bz2 Make archive of subset of dir/ and below
  find dir/ -name '*.txt' | xargs cp -a --target-directory=dir_txt/ --parents Make copy of subset of dir/ and below
  ( tar -c /dir/to/copy ) | ( cd /where/to/ && tar -x -p ) Copy (with permissions) copy/ dir to /where/to/ dir
  ( cd /dir/to/copy && tar -c . ) | ( cd /where/to/ && tar -x -p ) Copy (with permissions) contents of copy/ dir to /where/to/
  ( tar -c /dir/to/copy ) | ssh -C user@remote 'cd /where/to/ && tar -x -p' Copy (with permissions) copy/ dir to remote:/where/to/ dir
  dd bs=1M if=/dev/sda | gzip | ssh user@remote 'dd of=sda.gz' Backup harddisk to remote machine
rsync (Network efficient file copier: Use the --dry-run option for testing)
  rsync -P rsync://rsync.server.com/path/to/file file Only get diffs. Do multiple times for troublesome downloads
  rsync --bwlimit=1000 fromfile tofile Locally copy with rate limit. It's like nice for I/O
  rsync -az -e ssh --delete ~/public_html/ remote.com:'~/public_html' Mirror web site (using compression and encryption)
  rsync -auz -e ssh remote:/dir/ . && rsync -auz -e ssh . remote:/dir/ Synchronize current directory with remote one
ssh (Secure SHell)
  ssh $USER@$HOST command Run command on $HOST as $USER (default command=shell)
ssh -f -Y $USER@$HOSTNAME xeyes Run GUI command on $HOSTNAME as $USER
  scp -p -r $USER@$HOST: file dir/ Copy with permissions to $USER's home directory on $HOST
  scp -c arcfour $USER@$LANHOST: bigfile Use faster crypto for local LAN. This might saturate GigE
  ssh -g -L 8080:localhost:80 root@$HOST Forward connections to $HOSTNAME:8080 out to $HOST:80
  ssh -R 1434:imap:143 root@$HOST Forward connections from $HOST:1434 in to imap:143
  ssh-copy-id $USER@$HOST Install public key for $USER@$HOST for password-less log in
wget (multi purpose download tool)
(cd dir/ && wget -nd -pHEKk http://www.pixelbeat.org/cmdline.html) Store local browsable version of a page to the current dir
  wget -c http://www.example.com/large.file Continue downloading a partially downloaded file
  wget -r -nd -np -l1 -A '*.jpg' http://www.example.com/dir/ Download a set of files to the current directory
  wget ftp://remote/file[1-9].iso/ FTP supports globbing directly
wget -q -O- http://www.pixelbeat.org/timeline.html | grep 'a href' | head Process output directly
  echo 'wget url' | at 01:00 Download url at 1AM to current dir
  wget --limit-rate=20k url Do a low priority download (limit to 20KB/s in this case)
  wget -nv --spider --force-html -i bookmarks.html Check links in a file
  wget --mirror http://www.example.com/ Efficiently update a local copy of a site (handy from cron)
networking (Note ifconfig, route, mii-tool, nslookup commands are obsolete)
  ethtool eth0 Show status of ethernet interface eth0
  ethtool --change eth0 autoneg off speed 100 duplex full Manually set ethernet interface speed
  iwconfig eth1 Show status of wireless interface eth1
  iwconfig eth1 rate 1Mb/s fixed Manually set wireless interface speed
iwlist scan List wireless networks in range
ip link show List network interfaces
  ip link set dev eth0 name wan Rename interface eth0 to wan
  ip link set dev eth0 up Bring interface eth0 up (or down)
ip addr show List addresses for interfaces
  ip addr add 1.2.3.4/24 brd + dev eth0 Add (or del) ip and mask (255.255.255.0)
ip route show List routing table
  ip route add default via 1.2.3.254 Set default gateway to 1.2.3.254
host pixelbeat.org Lookup DNS ip address for name or vice versa
hostname -i Lookup local ip address (equivalent to host `hostname`)
whois pixelbeat.org Lookup whois info for hostname or ip address
netstat -tupl List internet services on a system
netstat -tup List active connections to/from system
windows networking (Note samba is the package that provides all this windows specific networking support)
smbtree Find windows machines. See also findsmb
  nmblookup -A 1.2.3.4 Find the windows (netbios) name associated with ip address
  smbclient -L windows_box List shares on windows machine or samba server
  mount -t smbfs -o fmask=666,guest //windows_box/share /mnt/share Mount a windows share
  echo 'message' | smbclient -M windows_box Send popup to windows machine (off by default in XP sp2)
text manipulation (Note sed uses stdin and stdout. Newer versions support inplace editing with the -i option)
  sed 's/string1/string2/g' Replace string1 with string2
  sed 's/\(.*\)1/\12/g' Modify anystring1 to anystring2
  sed '/ *#/d; /^ *$/d' Remove comments and blank lines
  sed ':a; /\\$/N; s/\\\n//; ta' Concatenate lines with trailing \
  sed 's/[ \t]*$//' Remove trailing spaces from lines
  sed 's/\([`"$\]\)/\\\1/g' Escape shell metacharacters active within double quotes
seq 10 | sed "s/^/      /; s/ *\(.\{7,\}\)/\1/" Right align numbers
  sed -n '1000{p;q}' Print 1000th line
  sed -n '10,20p;20q' Print lines 10 to 20
  sed -n 's/.*<title>\(.*\)<\/title>.*/\1/ip;T;q' Extract title from HTML web page
  sed -i 42d ~/.ssh/known_hosts Delete a particular line
  sort -t. -k1,1n -k2,2n -k3,3n -k4,4n Sort IPV4 ip addresses
echo 'Test' | tr '[:lower:]' '[:upper:]' Case conversion
tr -dc '[:print:]' < /dev/urandom Filter non printable characters
tr -s '[:blank:]' '\t' </proc/diskstats | cut -f4 cut fields separated by blanks
history | wc -l Count lines
set operations (Note you can export LANG=C for speed. Also these assume no duplicate lines within a file)
  sort file1 file2 | uniq Union of unsorted files
  sort file1 file2 | uniq -d Intersection of unsorted files
  sort file1 file1 file2 | uniq -u Difference of unsorted files
  sort file1 file2 | uniq -u Symmetric Difference of unsorted files
  join -t'\0' -a1 -a2 file1 file2 Union of sorted files
  join -t'\0' file1 file2 Intersection of sorted files
  join -t'\0' -v2 file1 file2 Difference of sorted files
  join -t'\0' -v1 -v2 file1 file2 Symmetric Difference of sorted files
math
echo '(1 + sqrt(5))/2' | bc -l Quick math (Calculate φ). See also bc
seq -f '4/%g' 1 2 99999 | paste -sd-+ | bc -l Calculate π the unix way
echo 'pad=20; min=64; (100*10^6)/((pad+min)*8)' | bc More complex (int) e.g. This shows max FastE packet rate
echo 'pad=20; min=64; print (100E6)/((pad+min)*8)' | python Python handles scientific notation
echo 'pad=20; plot [64:1518] (100*10**6)/((pad+x)*8)' | gnuplot -persist Plot FastE packet rate vs packet size
echo 'obase=16; ibase=10; 64206' | bc Base conversion (decimal to hexadecimal)
echo $((0x2dec)) Base conversion (hex to dec) ((shell arithmetic expansion))
units -t '100m/9.58s' 'miles/hour' Unit conversion (metric to imperial)
units -t '500GB' 'GiB' Unit conversion (SI to IEC prefixes)
units -t '1 googol' Definition lookup
seq 100 | (tr '\n' +; echo 0) | bc Add a column of numbers. See also add and funcpy
calendar
cal -3 Display a calendar
cal 9 1752 Display a calendar for a particular month year
date -d fri What date is it this friday. See also day
[ $(date -d "tomorrow" +%d) = "01" ] || exit exit a script unless it's the last day of the month
date --date='25 Dec' +%A What day does xmas fall on, this year
date --date='@2147483647' Convert seconds since the epoch (1970-01-01 UTC) to date
TZ='America/Los_Angeles' date What time is it on west coast of US (use tzselect to find TZ)
date --date='TZ="America/Los_Angeles" 09:00 next Fri' What's the local time for 9AM next Friday on west coast US
locales
printf "%'d\n" 1234 Print number with thousands grouping appropriate to locale
BLOCK_SIZE=\'1 ls -l Use locale thousands grouping in ls. See also l
echo "I live in `locale territory`" Extract info from locale database
LANG=en_IE.utf8 locale int_prefix Lookup locale info for specific country. See also ccodes
locale -kc $(locale | sed -n 's/\(LC_.\{4,\}\)=.*/\1/p') | less List fields available in locale database
recode (Obsoletes iconv, dos2unix, unix2dos)
recode -l | less Show available conversions (aliases on each line)
  recode windows-1252.. file_to_change.txt Windows "ansi" to local charset (auto does CRLF conversion)
  recode utf-8/CRLF.. file_to_change.txt Windows utf8 to local charset
  recode iso-8859-15..utf8 file_to_change.txt Latin9 (western europe) to utf8
  recode ../b64 < file.txt > file.b64 Base64 encode
  recode /qp.. < file.qp > file.txt Quoted printable decode
  recode ..HTML < file.txt > file.html Text to HTML
recode -lf windows-1252 | grep euro Lookup table of characters
echo -n 0x80 | recode latin-9/x1..dump Show what a code represents in latin-9 charmap
echo -n 0x20AC | recode ucs-2/x2..latin-9/x Show latin-9 encoding
echo -n 0x20AC | recode ucs-2/x2..utf-8/x Show utf-8 encoding
CDs
  gzip < /dev/cdrom > cdrom.iso.gz Save copy of data cdrom
  mkisofs -V LABEL -r dir | gzip > cdrom.iso.gz Create cdrom image from contents of dir
  mount -o loop cdrom.iso /mnt/dir Mount the cdrom image at /mnt/dir (read only)
  cdrecord -v dev=/dev/cdrom blank=fast Clear a CDRW
  gzip -dc cdrom.iso.gz | cdrecord -v dev=/dev/cdrom - Burn cdrom image (use dev=ATAPI -scanbus to confirm dev)
  cdparanoia -B Rip audio tracks from CD to wav files in current dir
  cdrecord -v dev=/dev/cdrom -audio -pad *.wav Make audio CD from all wavs in current dir (see also cdrdao)
  oggenc --tracknum='track' track.cdda.wav -o 'track.ogg' Make ogg file from wav file
disk space (See also FSlint)
ls -lSr Show files by size, biggest last
du -s * | sort -k1,1rn | head Show top disk users in current dir. See also dutop
du -hs /home/* | sort -k1,1h Sort paths by easy to interpret disk usage
df -h Show free space on mounted filesystems
df -i Show free inodes on mounted filesystems
fdisk -l Show disks partitions sizes and types (run as root)
rpm -q -a --qf '%10{SIZE}\t%{NAME}\n' | sort -k1,1n List all packages by installed size (Bytes) on rpm distros
dpkg-query -W -f='${Installed-Size;10}\t${Package}\n' | sort -k1,1n List all packages by installed size (KBytes) on deb distros
dd bs=1 seek=2TB if=/dev/null of=ext3.test Create a large test file (taking no space). See also truncate
> file truncate data of file or create an empty file
monitoring/debugging
tail -f /var/log/messages Monitor messages in a log file
strace -c ls >/dev/null Summarise/profile system calls made by command
strace -f -e open ls >/dev/null List system calls made by command
strace -f -e trace=write -e write=1,2 ls >/dev/null Monitor what's written to stdout and stderr
ltrace -f -e getenv ls >/dev/null List library calls made by command
lsof -p $$ List paths that process id has open
lsof ~ List processes that have specified path open
tcpdump not port 22 Show network traffic except ssh. See also tcpdump_not_me
ps -e -o pid,args --forest List processes in a hierarchy
ps -e -o pcpu,cpu,nice,state,cputime,args --sort pcpu | sed '/^ 0.0 /d' List processes by % cpu usage
ps -e -orss=,args= | sort -b -k1,1n | pr -TW$COLUMNS List processes by mem (KB) usage. See also ps_mem.py
ps -C firefox-bin -L -o pid,tid,pcpu,state List all threads for a particular process
ps -p 1,$$ -o etime= List elapsed wall time for particular process IDs
last reboot Show system reboot history
free -m Show amount of (remaining) RAM (-m displays in MB)
watch -n.1 'cat /proc/interrupts' Watch changeable data continuously
udevadm monitor Monitor udev events to help configure rules
system information (see also sysinfo) ('#' means root access is required)
uname -a Show kernel version and system architecture
head -n1 /etc/issue Show name and version of distribution
cat /proc/partitions Show all partitions registered on the system
grep MemTotal /proc/meminfo Show RAM total seen by the system
grep "model name" /proc/cpuinfo Show CPU(s) info
lspci -tv Show PCI info
lsusb -tv Show USB info
mount | column -t List mounted filesystems on the system (and align output)
grep -F capacity: /proc/acpi/battery/BAT0/info Show state of cells in laptop battery
# dmidecode -q | less Display SMBIOS/DMI information
# smartctl -A /dev/sda | grep Power_On_Hours How long has this disk (system) been powered on in total
# hdparm -i /dev/sda Show info about disk sda
# hdparm -tT /dev/sda Do a read speed test on disk sda
# badblocks -s /dev/sda Test for unreadable blocks on disk sda
interactive (see also linux keyboard shortcuts)
readline Line editor used by bash, python, bc, gnuplot, ...
screen Virtual terminals with detach capability, ...
mc Powerful file manager that can browse rpm, tar, ftp, ssh, ...
gnuplot Interactive/scriptable graphing
links Web browser
xdg-open . open a file or url with the registered desktop application
Command Description
grep . /proc/sys/net/ipv4/* List the contents of flag files
set | grep $USER Search current environment
tr '\0' '\n' < /proc/$$/environ Display the startup environment for any process
echo $PATH | tr : '\n' Display the $PATH one per line
kill -0 $$ && echo process exists and can accept signals Check for the existence of a process (pid)
find /etc -readable | xargs less -K -p'*ntp' -j $((${LINES:-25}/2)) Search paths and data with full context. Use n to iterate
Low impact admin
# apt-get install "package" -o Acquire::http::Dl-Limit=42 \
-o Acquire::Queue-mode=access
Rate limit apt-get to 42KB/s
  echo 'wget url' | at 01:00 Download url at 1AM to current dir
# apache2ctl configtest && apache2ctl graceful Restart apache if config is OK
nice openssl speed sha1 Run a low priority command (openssl benchmark)
renice 19 -p $$; ionice -c3 -p $$ Make shell (script) low priority. Use for non interactive tasks
Interactive monitoring
watch -t -n1 uptime Clock with system load
htop -d 5 Better top (scrollable, tree view, lsof/strace integration, ...)
iotop What's doing I/O
# watch -d -n30 "nice ps_mem.py | tail -n $((${LINES:-12}-2))" What's using RAM
# iftop What's using the network. See also iptraf
# mtr www.pixelbeat.org ping and traceroute combined
Useful utilities
pv < /dev/zero > /dev/null Progress Viewer for data copying from files and pipes
wkhtml2pdf http://.../linux_commands.html linux_commands.pdf Make a pdf of a web page
timeout 1 sleep 3 run a command with bounded time. See also timeout
Networking
python -m SimpleHTTPServer Serve current directory tree at http://$HOSTNAME:8000/
openssl s_client -connect www.google.com:443 </dev/null 2>&0 |
openssl x509 -dates -noout
Display the date range for a site's certs
curl -I www.pixelbeat.org Display the server headers for a web site
# lsof -i tcp:80 What's using port 80
# httpd -S Display a list of apache virtual hosts
vim scp://user@remote//path/to/file Edit remote file using local vim. Good for high latency links
curl -s http://www.pixelbeat.org/pixelbeat.asc | gpg --import Import a gpg key from the web
tc qdisc add dev lo root handle 1:0 netem delay 20msec Add 20ms latency to loopback device (for testing)
tc qdisc del dev lo root Remove latency added above
Notification
echo "DISPLAY=$DISPLAY xmessage cooker" | at "NOW +30min" Popup reminder
notify-send "subject" "message" Display a gnome popup notification
  echo "mail -s 'go home' P@draigBrady.com < /dev/null" | at 17:30 Email reminder
  uuencode file name | mail -s subject P@draigBrady.com Send a file via email
  ansi2html.sh | mail -a "Content-Type: text/html" P@draigBrady.com Send/Generate HTML email
Better default settings (useful in your .bashrc)
# tail -s.1 -f /var/log/messages Display file additions more responsively
seq 100 | tail -n $((${LINES:-12}-2)) Display as many lines as possible without scrolling
# tcpdump -s0 Capture full network packets
Useful functions/aliases (useful in your .bashrc)
md () { mkdir -p "$1" && cd "$1"; } Change to a new directory
strerror() { python -c "import os; print os.strerror($1)"; } Display the meaning of an errno
plot() { { echo 'plot "-"' "$@"; cat; } | gnuplot -persist; } Plot stdin. (e.g: • seq 1000 | sed 's/.*/s(&)/' | bc -l | plot)
hili() { e="$1"; shift; grep --col=always -Eih "$e|$" "$@"; } highlight occurences of expr. (e.g: • env | hili $USER)
alias hd='od -Ax -tx1z -v' Hexdump. (usage e.g.: • hd /proc/self/cmdline | less)
alias realpath='readlink -f' Canonicalize path. (usage e.g.: • realpath ~/../$USER)
Multimedia
DISPLAY=:0.0 import -window root orig.png Take a (remote) screenshot
convert -filter catrom -resize '600x>' orig.png 600px_wide.png Shrink to width, computer gen images or screenshots
  mplayer -ao pcm -vo null -vc dummy /tmp/Flash* Extract audio from flash video to audiodump.wav
  ffmpeg -i filename.avi Display info about multimedia file
ffmpeg -f x11grab -s xga -r 25 -i :0 -sameq demo.mpg Capture video of an X display
DVD
  for i in $(seq 9); do ffmpeg -i $i.avi -target pal-dvd $i.mpg; done Convert video to the correct encoding and aspect for DVD
  dvdauthor -odvd -t -v "pal,4:3,720xfull" *.mpg;dvdauthor -odvd -T Build DVD file system. Use 16:9 for widescreen input
  growisofs -dvd-compat -Z /dev/dvd -dvd-video dvd Burn DVD file system to disc
Unicode
python -c "import unicodedata as u; print u.name(unichr(0x2028))" Lookup a unicode character
uconv -f utf8 -t utf8 -x nfc Normalize combining characters
printf '\300\200' | iconv -futf8 -tutf8 >/dev/null Validate UTF-8
printf 'ŨTF8\n' | LANG=C grep --color=always '[^ -~]\+' Highlight non printable ASCII chars in UTF-8
fc-match -s "sans:lang=zh" List font match order for language and style
Development
gcc -march=native -E -v -</dev/null 2>&1|sed -n 's/.*-mar/-mar/p' Show autodetected gcc tuning params. See also gcccpuopt
for i in $(seq 4); do { [ $i = 1 ] && wget http://url.ie/6lko -qO-||
./a.out; } | tee /dev/tty | gcc -xc - 2>/dev/null; done
Compile and execute C code from stdin
cpp -dM /dev/null Show all predefined macros
echo "#include <features.h>" | cpp -dN | grep "#define __USE_" Show all glibc feature macros
  gdb -tui Debug showing source code context in separate windows
Extended Attributes (Note you may need to (re)mount with "acl" or "user_xattr" options)
getfacl . Show ACLs for file
setfacl -m u:nobody:r . Allow a specific user to read file
setfacl -x u:nobody . Delete a specific user's rights to file
  setfacl --default -m group:users:rw- dir/ Set umask for a for a specific dir
  getcap file Show capabilities for a program
  setcap cap_net_raw+ep your_gtk_prog Allow gtk program raw access to network
stat -c%C . Show SELinux context for file
  chcon ... file Set SELinux context for file (see also restorecon)
getfattr -m- -d . Show all extended attributes (includes selinux,acls,...)
setfattr -n "user.foo" -v "bar" . Set arbitrary user attributes
BASH specific
echo 123 | tee >(tr 1 a) | tr 1 b Split data to 2 commands (using process substitution)
  meld local_file <(ssh host cat remote_file) Compare a local and remote file (using process substitution)
Multicore
taskset -c 0 nproc Restrict a command to certain processors
find -type f -print0 | xargs -r0 -P$(nproc) -n10 md5sum Process files in parallel over available processors
  sort -m <(sort data1) <(sort data2) >data.sorted Sort separate data files over 2 processors
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