Linux Tricks and Useful Commands

pwd -P # Print path to the dir you are in, converting any symlinks in the path into their real/(P)hysical directory name.
grep -ril inactive /etc # Show matching files(-l) with the string “inactive” regardless of case(-i) in all subdirs of /etc (-r)

for i in {0..365};do date -d “Jan 1 2012 + $i day” +”*%B %_d – “; done # Generate days of the year list with some formatting. Req. GNU date

sox song.wav -t wav – pitch 1200 | play – # Play a song an octave higher without saving an intermediary file. 1200 cents == 1 octave

ascii || man ascii # Quick access to the ASCII character table either through the ascii program or the man page if you don’t have the prog.

ionice -c 3 cp vm1.img vm1-clone.img # Copy a file using “ionice -c 3” to give it idle IO priority to reduce load on the system.

mv somedata{,-20120720} # This is the same as mv somedata somedata-20120720 but is shorter. You don’t have to type somedata twice.

foremost # Foremost is a file recovery program that can extract files from disk images and more. # GNU ddrescue is a good tool for copying/recovering disk images.

dd if=/dev/sdc of=sdc.img bs=100M conv=sync,noerror # Image a disk, sync,noerror will continue on read errors and pad missing parts.
kill -USR1 $( pidof dd ) # Tell each dd process to print its current status (blocks written, etc). dd interprets the USR1 signal this way.

ls -d */ # View only the directories in the current directory. The / at the end of the wildcard makes this work.

convert -rotate -90 sideways.jpg rightsideup.jpg # Rotate an image 90 degrees counterclockwise. The convert command is from ImageMagick

gzip -l largefile.gz # A fast way to get the size of the uncompressed gzip file. However the uncompressed value can’t be more than 4GB.

montage -geometry 800×600+4+4 pic1.jpg pic2.jpg pic3.jpg pic4.jpg -tile x2 combined.jpg # Make 2×2 800×600 montage with 4 px border.

echo “1-800-SHOWNUM” | tr A-Z a-z | tr ‘a-z’ ‘22233344455566677778889999’ # Looks like a command that we could make shorter

[Ctrl-w] # Remove the previous word on the command line (before the cursor). This is highly useful when reusing old commands.

[Ctrl-l] # This is usually equivilent to running ‘clear’. Its usually quicker and doesn’t leave the command in your command line history.

[Ctrl-e] # Move your cursor to the end of the line. Faster than holding down right arrow

[Ctrl-a] # Move your cursor to the beginning of the line. Faster than holding down left arrow. In screen, you need to press

[Ctrl-r]string # Reverse search through your command history for ‘string’. Press Ctrl-r again to continue searching backwards. ESC when done

cd # Takes you back to your home directory.

cd – # Takes you back to the previous directory you were in. Good to know if you don’t already.

for d in /dev/sd? ; do sudo smartctl -H $d ; done # How are your drives doing? may need apt-get install smartmontools Thx

find dir1 dir2 dir3 | wc -l # Count the number of files in multiple directories.

echo “kernel.panic = 20” | sudo tee -a /etc/sysctl.conf # so your headless Linux system reboots after a kernel panic (20 sec) Thx

getent services 993 # Look up in your services table to see what port 993 is. Can also look up by service name to get port.

ls -1 | tr A-Z a-z # List files and print them all in lowercase so you can copy and paste and compare with another list that got fatty.

getent passwd|while IFS=: read -r user n uid n n home n;do if [[ $uid -ge 500 ]];then printf “$user “;du -sh $home;fi;done # space per user

sleep 8h 30m 20 # In the GNU version of sleep you provide mixed time intervals to stack them together instead of just seconds.

sed -n ‘1,10p’ # Probably your best option is to put something like this into a script called or whatever

ls -ltrah | sponge | pee head tail # This also works. sponge also comes with moreutils and kinda fits with the naming there.

ls -ltrah | pee “sed -n ‘1,10p'” tail # Sorry, the last command suffers from head closing the input prematurely. So try this instead. # iodine is a client and server that allow you to tunnel IP traffic over DNS, bypassing many firewalls, etc.

alias dnsip=’dig +short’ # even gets your public ip behind pay hotspots.
df . # This is an easy way to find out what partition the current directory is on, regardless of symlinks.

curl “” |python -mjson.tool |grep ‘”text”:’ # Reformat JSON data and get latest updates
identify -format “%f F:%[EXIF:Flash]\n” *.jpg | egrep ” F:(0|16|24|32)$” # Show photo filenames where no flash was used.

identify -format “%f F:%[EXIF:Flash]\n” *.jpg | egrep ” F:(0|16|24|32)$” # Show photo filenames where no flash was used.
/usr/lib/xscreensaver/skyrocket # More fireworks! GUI output, but many CLI options. You need the rss-glx screensavers package.

date -d “$(grep finish /proc/mdstat |sed -e ‘s/^.*finish=//;s/ .*$//;s/\..*$//’)min” # Figure out when your md-raid will finish.

todo(){ cd ~/.todo||return 1&& l=$(ls -1t|head -n1)&&t=$(date +%Y%m%d);[[ “$1” == “last” ]]&&cp $l $t; ${EDITOR:-vi} $t;cd -;} # Todo list.

ls -l |sed ‘s/^/ /’ # Ever have one of those situations in console mode where you can’t read the first characters? This intents the output.

fsck -y /dev/sda1 || echo “You’re fscked!” | mail -s alert # Use || when you want to run a command only if the first one failed

service network start && service httpd start # Use && when you want to run a command after another only if the first one is successful

sleep 30m ; killall tcpdump # Use a ; in a statement if you want to run a command after another, but don’t care about the exit status of 1st
ssh-copy-id ‘user@remotehost’ # Automatically installs your public key to the remote host (this actually is included in the openssh package)

xargs -n1 -0 < /proc/$(pidof firefox| cut -d’ ‘ -f1)/environ # Print the environment of a running process (ie. firefox) awk ‘{if (a[$1]) { print; } else { a[$1]=1 }}’ md5sums.txt # And here is a way to print only duplicates using just awk. sort md5sums.txt | uniq -d -w 32 # Print only duplicate md5sums by looking only at first 32 chars for uniqueness. head -5 file1 |cat – file2 >combofile # One way of putting the first 5 lines of file1 before the contents of file2 and writing to combofile

last |awk ‘BEGIN {f=0;u=”YOURUSER”;} {if ($1==u && f==0){f=1; print $0;}else if(f==1 && $1!=u) {print $0;exit;}}’ # Display prev. user b4 u

grep -B2 Subj: maildrop.log | grep -v ^From: | grep -v ^– | xargs -d$’\n’ -n 2 # Join the Date and Subj line together in procmail log.

find . -type f | egrep -o “[^\.]+$” | tr A-Z a-z | sort | uniq -c # Show a count of all the file extensions in use below current directory.

awk ‘{a[$1] += $10} END {for (h in a) print h ” ” a[h]}’ access_log | sort -k 2 -nr | head -10 # Display top bandwidth hogs on website.

curl -s ‘…’ |grep -q ‘#500’ && echo “500 ready”|mail -s 500 you # site watcher

– ssh-keygen -R servername # Remove the host key for ‘servername’ from your known_hosts file. This is now the proper way to do it.

Next I’ll be showing 4+ different ways of doing the same thing, printing out the partition table entries for use in snmpd.conf.

df -TP | grep -E ” ext[34] ” | awk {‘print $NF’} | sed ‘s/.*/disk & 5%/’ # Print out the partition table and format it for snmpd.conf

df -TP | awk ‘$2=/ext[34]/ {print “disk ” $NF ” 5%”}’ # snmpd disk entries, same thing but let awk do most of the processing work.

df -P -t ext3 -t ext4 | grep / | awk ‘{print “disk ” $NF ” 5%”}’ # snmpd disk entries, Let df select the filesystems directly.

ethtool -p eth0 # Blink eth0’s LED so you can find it in the rat’s next of server cables. Ctrl-C to stop. Thanks

ls / fake 2>&1 > /dev/null | grep “cannot” # Redirect stdout to /dev/null, and make stderr go through the pipe.

df -TP | grep -E ” ext[34] ” | rev | cut -d’ ‘ -f1 | rev | while read -r fs ; do echo “disk $fs 5%” ; done # Disk entries. The Crazy Way!

ps aux | awk ‘/firefox/ {sum += $6} END { printf “%dMB\n”, sum/1024 }’ # Show the total memory used by Firefox processes (Probably a lot)

Tip ~ To test Internet connection speed from console over SSH command line:
## Download speed
lftp -e ‘pget; exit; ‘

## Upload speed
lftp -u userName -e ‘put largecd1.avi; bye’

## Get network throughput rate between two Linux or Unix servers:
iperf -s -B serverIP
iperf -c serverIP -d -t 60 -i 10

See for more info –

* More tips and howtos from our /faq/ section *
Debian / Ubuntu: Console Based Network Load Monitor or see a quick video demo –

Debian / Ubuntu Python: Set Planet Venus To Combine Two Or More RSS Feeds

OpenBSD: Boot / Install Using PXE (Preboot Execution Environment)

HowTo: Bash Extract Filename And Extension In Unix / Linux

HowTo: Bash Shell Split String Into Array

Sed: Find and Replace The Whole Line [ Regex ]

Bash Script: Find Out In What Directory Script Is Stored Under Unix Or Linux

find . -newerBt “24 hours ago” # Find files created in the last 24 hours. Note: This won’t work on all filesystems.

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