Linux Cheat Sheet
My linux cheat Sheet base on Ubuntu
basic¶
# create multi line file
cat <<EOT > multi_line_file.txt
line1
line2
EOT
# create multi line file with tee
sudo tee -a ~/.ssh/config << EOF
Host localhost
ForwardAgent yes
EOF
# check memory usage
htop
free -h
awk¶
# skip first line, useful for skip colume name
awk 'NR!=1 {print}'
# filter when colume one not match regex pattern
awk '$1 !~ /^some-regex-pattern$/ {print}')
# print colume 1, 2 and added "|" in between
awk '{print $1"|"$2}')
# print with right padding space
awk '{printf "%-20s %-20s\n",$1,$2}'
ssh¶
# gen key pair (id_rsa, id_rsa.pub) in folder `/home/admin/.ssh/`
ssh-keygen
# upload key for login (append key to user@remote_host:~/.ssh/authorized_keys)
ssh-copy-id user@remote_host
# ssh tunnel
ssh user@remote_host -L <local_port>:<target_host>:<target_port>
# scp upload folder
scp -r "~/some_folder" user@remote_host:~/
sync time with hk ntp server¶
# create config file
mkdir -p /etc/systemd/timesyncd.conf.d/
cat <<EOT > /etc/systemd/timesyncd.conf.d/hk_ntp.conf
[Time]
NTP=stdtime.gov.hk
EOT
# set timezone
timedatectl set-timezone 'Asia/Hong_Kong'
# restart timesyncd service
systemctl restart systemd-timesyncd
# check status
timedatectl timesync-status
timedatectl show-timesync
IPv6 users may also access NTP service through time.hko.hk
add apt repo¶
# add repo
echo "deb http://tw.archive.ubuntu.com/ubuntu/ jammy main" > /etc/apt/sources.list.d/apt_tw_mirror.list
apt update
deb [ option1=value1 option2=value2 ] uri suite [component1] [component2] [...]
deb:debordeb-src, deb-src means include source code, only used when you want to modify source codeuri: repo uri, launchpad provides some repo heresuite: usually use ubuntu version code name herecomponent: usually have four option- main - Officially supported software
- restricted - Supported software that is not available under a completely free license.
- universe - Community maintained software, i.e. not officially supported software.
- multiverse - Software that is not free
extend disk size¶
# check total dir size
du -sh /var/*
# check disk size
df -h
# expand vm linux disk
sudo apt install parted
sudo parted -l
(parted) resizepart 1 100%
(parted) quit
sudo resize2fs /dev/sda
extend disk size (with logical volume manager)¶
# ref: https://packetpushers.net/ubuntu-extend-your-default-lvm-space/
# rescan disk size
echo 1 | sudo tee /sys/class/block/sda/device/rescan
# resize disk
sudo cfdisk # step: resize > write > quit
# resize pv
sudo pvresize /dev/sda3
# extend logical volumes
sudo lvextend -l +100%FREE /dev/ubuntu-vg/ubuntu-lv
# display lv
sudo lvdisplay
# resize filesystem
sudo resize2fs /dev/mapper/ubuntu--vg-ubuntu--lv
disable swap and kswapd0¶
# edit file `/etc/fstab` and comment swap line
sudo vim /etc/fstab
## /swap.img none swap sw 0 0
# turnoff swap
swapoff -a
# checking
free -h
# 0 swappiness really prevents from any swapping even if there is a swap storage available
echo 'vm.swappiness=0' | sudo tee /etc/sysctl.d/swappiness_zero.conf
# reload all sysctl config
sysctl --system
# search swap unit
systemctl list-units *swap* --all
# mask and stop swap unit permanently
systemctl mask swap.target
systemctl stop swap.target
# verify
free -m
sysctl vm.swappiness
systemctl status *swap* --all
ref: kernel swappiness
find command¶
# search log file
find /var/log -iname '*.log' -type f
# search dir
find $HOME -iname 'php' -type d
# search file bigger than 10MiB
find $HOME -type f -size +10M
# search file created more than 7 days
find $HOME -type f -ctime +7
# search file modified within 60 mins
find $HOME -type f -mmin -60
# move
find $HOME -type f -name "*.txt" -exec move {} ./new_dir/ \;
archive log files¶
# zip log file
find /var/log -regextype posix-egrep -regex '.*/.*([0-9]{8})$' -exec gzip {} \;
# move ziped log files to other folder with same dir structure
LOG_ARCHIVED_FOLDER=/mnt/data/log_archived/
cd /var/log
find . -type d -exec mkdir -p "$LOG_ARCHIVED_FOLDER/{}" \;
find . -type f -name '*.gz' -exec mv --backup "{}" "$LOG_ARCHIVED_FOLDER/{}" \;