Update 30 DEC 2015
Create empty file or empty existing one:
> test.txt
Update date from Ubuntu NTP server:
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:
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):
watch ps -ef
List all users:
getent passwd
Mount root in read/write mode:
mount -o remount,rw /
Mount a directory (for cases when symlinking will not work):
mount --bind /source /destination
Send dynamic update to DNS server:
nsupdate < <EOF update add $HOST 86400 A $IP send EOF
Recursively grep all directories:
grep -r "some_text" /path/to/dir
List ten largest open files:
lsof / | awk '{ if($7 > 1048576) print $7/1048576 "MB "$9 }' | sort -n -u | tail
Show free RAM in MB:
free -m | grep cache | awk '/[0-9]/{ print $4" MB" }'
Open Vim and jump to end of file:
vim + some_file_name
Git clone specific branch (master):
git clone git@github.com:name/app.git -b master
Git switch to another branch (develop):
git checkout develop
Git delete branch (myfeature):
git branch -d myfeature
Git delete remote branch:
git push origin :branchName
Git push new branch to remote:
git push -u origin mynewfeature
Print out the last cat command from history:
!cat:p
Run your last cat command from history:
!cat
Find all empty subdirectories in /home/user:
find /home/user -maxdepth 1 -type d -empty
Get all from line 50 to 60 in test.txt:
< test.txt sed -n '50,60p'
Run last command (if it was: mkdir /root/test, below will run: sudo mkdir /root/test):
sudo !!
Create temporary RAM filesystem – ramdisk (first create /tmpram directory):
mount -t tmpfs tmpfs /tmpram -o size=512m
Grep whole words:
grep -w "name" test.txt
Append text to a file that requires raised privileges:
echo "some text" | sudo tee -a /path/file
List all supported kill signals:
kill -l
Generate random password (16 characters long in this case):
openssl rand -base64 16
Do not log last session in bash history:
kill -9 $$
Scan network to find open port:
nmap -p 8081 172.20.0.0/16
Set git email:
git config --global user.email "me@example.com"
To sync with master if you have unpublished commits:
git pull --rebase origin master
Move all files with “txt” in name to /home/user:
find -iname "*txt*" -exec mv -v {} /home/user \;
Put the file lines side by side:
paste test.txt test1.txt
Progress bar in shell:
pv data.log
Send the data to server with netcat:
echo "hosts.sampleHost 10 `date +%s`" | nc 192.168.200.2 3000
Convert tabs to spaces:
expand test.txt > test1.txt
Skip bash history:
< <space>>cmd
Go to the previous working directory:
cd -
Split large tar.gz archive (100MB each) and put it back:
split –b 100m /path/to/large/archive /path/to/output/files cat files* > archive
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