The-Useful-Linux-Commands-Compedium.md

Searching

Search files with a certain extension for a specific string

find . -name "*.php" -exec grep -H "217.156.XXX.XXX" {} \;

Search files older than X days and delete them

find /var/log/.../*.log -mtime +3 -exec rm {} \;

Searching in files over several lines

pcregrep -Mo '<sometag>\n.+</lang>' ./* > sometag.txt

Replace string in file

sed -i.bak 's$//breezee.co$//api.breezee.co$g' js/sync.js

Package Management

Keep apt from updating a package

apt-mark hold package_name

MySQL

Skip replication error

STOP SLAVE;
SET GLOBAL SQL_SLAVE_SKIP_COUNTER = 1; 
START SLAVE;
SHOW SLAVE STATUS;

Skip certain replication error code

nano /etc/mysql/my.cnf
slave-skip-errors = 1062

Software RAID

Drive replacement (after rescue boot)

# copy partition tables
sgdisk -R /dev/sda /dev/sdb
sgdisk -G /dev/sda
sfdisk -d /dev/sdb | sfdisk /dev/sda

# add the ew
mdadm /dev/md0 -a /dev/sda1
mdadm /dev/md1 -a /dev/sda2
mdadm /dev/md2 -a /dev/sda3
mdadm /dev/md3 -a /dev/sda4

cat /proc/mdstat

mount /dev/md2 /mnt/rescue
mount /dev/md1 /mnt/rescue/boot
chroot-prepare /mnt/rescue
chroot /mnt/rescue /bin/bash

grub-install /dev/sda

Networking

See what's listening on a specific port

lsof -i tcp:3306

Sample output:

COMMAND   PID   USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
Spotify 10865 lucian   71u  IPv4 0x58cb978a7668824d      0t0  TCP 192.168.89.0:63871->118.240.199.104.bc.googleusercontent.com:http (ESTABLISHED)

Others

Locale setting

export LANGUAGE=en_US.UTF-8
export LANG=en_US.UTF-8
export LC_ALL=en_US.UTF-8
locale-gen en_US.UTF-8
sudo dpkg-reconfigure locales