Linux

Below you can found a list of commands that saved my life in certain critical conditions. I hope that these commands can help you if you are in the same condition.

Networking

Get MAC address of a network card (version 1)

ifconfig eth0 | grep -o -E '([[:xdigit:]]{1,2}:){5}[[:xdigit:]]{1,2}'

Get MAC address of a network card (version 2)

ifconfig eth0 | awk '/HWaddr/ {print $5}'

List network card names

basename -a /sys/class/net/* 

List TCP open file

lsof -i4 -P

Storage, Disk and files

Disk usage without mount points

du -hx

How to less last file in a directory ?

ls -1 -t | head -1 | xargs less

List file using ls command with full path

ls -1 $PWD/filename.ext

Exclude from listing file with particular extension

ls -dl !(*.xml|*.txt|*.pdf|*.sql)

Create a file with a specific size

truncate -s 14M filename

Follow a pathname until a terminal point is found

namei /var/log

Information about mountpoint

findmnt /mnt/mountpoint

User Management

Force user to change password at first logon

chage -d 0 {username}

Miscellaneous

Perfoming line wrap for long context

echo "very long line with some text" | fold -w 5

Protect a zip file on command line.

zip -e "file_name".zip "list_of_files"

Format date in another locale

LC_ALL=us date -d'now-2 hours' +'%b %d %H:%M'

Execute local bash script on remote host

ssh user@host 'bash -s'  < local.cmd

Get authentication failure from /var/log/auth.log

grep "authentication failure;" /var/log/auth.log | \
  egrep -o "[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}" | \
  sort | uniq -c | sort -nr | less 

Append current date to a file every 1 second

nohup bash -c "while sleep 1; do date >> /home/user/test.txt; done" & 

Force logrotate

logrotate --force $CONFIG_FILE 

Rsync data

rsync -av /var/lib/mysql /mnt/mysql/ 

Send test mail

echo "Subject: sendmail test" | sendmail -v [email protected]

Create symbolic or hard link with cp command

cp -s source dest # for symbolic link

cp -l source dest # for hard link

Read password from input and output hashed version

echo -n "Enter Password: " && head -1 < /dev/stdin | tr -d '\n' | sha256sum | cut -d " " -f1

Extract a specific file from an archive:

unzip -j path/to/archive.zip path/to/file_in_archive1 path/to/file_in_archive2