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...
Thursday, March 29, 2012
An A-Z Index of the Bash command line for Linux
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.
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.
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
Thursday, May 5, 2011
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 $HOME directory |
(cd dir && command) | Go to dir, execute command and return to current dir | |
• | pushd . | Put current dir on stack so you can popd back to it |
file searching | ||
• | alias l='ls -l --color=auto' | quick dir listing |
• | ls -lrt | List files by date. See also newest and find_mm_yyyy |
• | ls /usr/bin | pr -T9 -W$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 |