Linux shell tips and tricks
Send process to background:
Ctrl + z
Move process to foreground:
fg
Generate random hex number where n is number of characters:
openssl rand -hex n
Execute commands from a file in the current shell:
source /home/user/file.name
Substring for first 5 characters:
${variable:0:5}
SSH debug mode:
ssh -vvv user@ip_address
SSH with pem key:
ssh user@ip_address -i key.pem
Get complete directory listing to local directory with wget:
wget -r --no-parent --reject "index.html*" http://hostname/ -P /home/user/dirs
Create multiple directories:
mkdir -p /home/user/{test,test1,test2}
List processes tree with child processes:
ps axwef
Create war file:
jar -cvf name.war file
Test disk write speed:
dd if=/dev/zero of=/tmp/output.img bs=8k count=256k; rm -rf /tmp/output.img
Test disk read speed:
hdparm -Tt /dev/sda
Get md5 hash from text:
echo -n "text" | md5sum
Check xml syntax:
xmllint --noout file.xml
Extract tar.gz in new directory:
tar zxvf package.tar.gz -C new_dir
Get HTTP headers with curl:
curl -I http://www.example.com
Modify timestamp of some file or directory (YYMMDDhhmm):
touch -t 0712250000 file
Download from ftp using wget:
wget -m ftp://username:password@hostname
Generate random password (16 char long in this case):
LANG=c < /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c${1:-16};echo;
Quickly create a backup of a file:
cp some_file_name{,.bkp}
Access Windows share:
smbclient -U "DOMAIN\user" //dc.domain.com/share/test/dir
Run command from history (here at line 100):
!100
Unzip to directory:
unzip package_name.zip -d dir_name
Multiline text (CTRL + d to exit):
cat > test.txt
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 /
