Linux shell tips and tricks
Contents
I’m using Linux shell on daily basis, but I often forgot some useful command or shell tip. Yes, I can remember commands, but I can’t say that if I used it just once for specific task. Then I started to write Linux shell tips in text file on my Dropbox account and now I decided to share that. This list will be updated over time. Also keep in mind that for some tips you will need to install additional software on your Linux distribution.
UPDATE: June 15, 2013
Send process to background:
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Ctrl + z |
Move process to foreground:
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fg |
Generate random hex number where n is number of characters:
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openssl rand -hex n |
Execute commands from a file in the current shell:
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source /home/user/file.name |
Substring for first 5 characters:
1 2 3 4 |
${variable:0:5} |
SSH debug mode:
1 2 3 4 |
ssh -vvv user@ip_address |
SSH with pem key:
1 2 3 4 |
ssh user@ip_address -i key.pem |
Get complete directory listing to local directory with wget:
1 2 3 4 |
wget -r --no-parent --reject "index.html*" http://hostname/ -P /home/user/dirs |
Create multiple directories:
1 2 3 4 |
mkdir -p /home/user/{test,test1,test2} |
List processes tree with child processes:
1 2 3 4 |
ps axwef |
Create war file:
1 2 3 4 |
jar -cvf name.war file |
Test disk write speed:
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dd if=/dev/zero of=/tmp/output.img bs=8k count=256k; rm -rf /tmp/output.img |
Test disk read speed:
1 2 3 4 |
hdparm -Tt /dev/sda |
Get md5 hash from text:
1 2 3 4 |
echo -n "text" | md5sum |
Check xml syntax:
1 2 3 4 |
xmllint --noout file.xml |
Extract tar.gz in new directory:
1 2 3 4 |
tar zxvf package.tar.gz -C new_dir |
Get web headers with curl:
1 2 3 4 |
curl -v -D - http://hostname -o /dev/null |
Modify timestamp of some file or directory (YYMMDDhhmm):
1 2 3 4 |
touch -t 0712250000 file |
Download from ftp using wget:
1 2 3 4 |
wget -m ftp://username:password@hostname |
Generate random password (16 char long in this case):
1 2 3 4 |
LANG=c < /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c${1:-16};echo; |
Quickly create a backup of a file:
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cp some_file_name{,.bkp} |
Access Windows share:
1 2 3 4 |
smbclient -U "DOMAINuser" //dc.domain.com/share/test/dir |
Run command from history (here at line 100):
1 2 3 4 |
!100 |
Unzip to directory:
1 2 3 4 |
unzip package_name.zip -d dir_name |
Multiline text (CTRL + d to exit):
1 2 3 4 |
cat > test.txt |
Create empty file or empty existing one:
1 2 3 4 |
> test.txt |
Update date from Ubuntu NTP server:
1 2 3 4 5 6 7 8 |
ntpdate ntp.ubuntu.com netstat show all tcp4 listening ports: netstat -lnt4 | awk '{print $4}' | cut -f2 -d: | grep -o '[0-9]*' |
Convert image from qcow2 to raw:
1 2 3 4 5 6 |
qemu-img convert -f qcow2 -O raw precise-server-cloudimg-amd64-disk1.img precise-server-cloudimg-amd64-disk1.raw |
Run command repeatedly, displaying it’s output (default every two seconds):
1 2 3 4 |
watch ps -ef |
List all users:
1 2 3 4 |
getent passwd |
Mount root in read/write mode:
1 2 3 4 |
mount -o remount,rw / |
Mount a directory (for cases when symlinking will not work):
1 2 3 4 |
mount --bind /source /destination |
Send dynamic update to DNS server:
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nsupdate <<EOF update add $HOST 86400 A $IP send EOF |
Recursively grep all directories:
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grep -r "some_text" /path/to/dir |
List ten largest open files:
1 2 3 4 |
lsof / | awk '{ if($7 > 1048576) print $7/1048576 "MB "$9 }' | sort -n -u | tail |
Show free RAM in MB:
1 2 3 4 |
free -m | grep cache | awk '/[0-9]/{ print $4" MB" }' |
Open Vim and jump to end of file:
1 2 3 4 |
vim + some_file_name |
Git clone specific branch (master):
1 2 3 4 |
git clone git@github.com:name/app.git -b master |
Git switch to another branch (develop):
1 2 3 4 |
git checkout develop |
Git delete branch (myfeature):
1 2 3 4 |
git branch -d myfeature |
Git delete remote branch:
1 2 3 4 |
git push origin :branchName |
Git push new branch to remote:
1 2 3 4 |
git push -u origin mynewfeature |
Print out the last cat command from history:
1 2 3 4 |
!cat:p |
Run your last cat command from history:
1 2 3 4 |
!cat |
Find all empty subdirectories in /home/user:
1 2 3 4 |
find /home/user -maxdepth 1 -type d -empty |
Get all from line 50 to 60 in test.txt:
1 2 3 4 |
< test.txt sed -n '50,60p' |
Run last command (if it was: mkdir /root/test, below will run: sudo mkdir /root/test):
1 2 3 4 |
sudo !! |
Create temporary RAM filesystem – ramdisk (first create /tmpram directory):
1 2 3 4 |
mount -t tmpfs tmpfs /tmpram -o size=512m |
Grep whole words:
1 2 3 4 |
grep -w "name" test.txt |
UPDATE: June 15, 2013