My linux cheat Sheet base on Ubuntu

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}'

basic#

# create multi line file
cat <<EOT > multi_line_file.txt
line1
line2
EOT

# scp upload folder
scp -r "~/some_folder" user@remote_host:~/

# upload key for login
scp "~/.ssh/id_rsa.pub" user@remote_host:~/.ssh/authorized_keys

# ssh tunnel
ssh user@remote_host -L <local_port>:<target_host>:<target_port>

# check memory usage
htop
free -h

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: deb or deb-src, deb-src means include source code, only used when you want to modify source code
  • uri: repo uri, launchpad provides some repo here
  • suite: usually use ubuntu version code name here
  • component: 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
# 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

disable swap and kswapd0#

# turnoff swap
swapoff -a

# 0 swappiness really prevents from any swapping even if there is a swap storage available
echo 'vm.swappiness=0' > /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#

Linux manual page - find

# 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 "test.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/{}" \;

skip sudo password#

echo "$USER ALL=(ALL) NOPASSWD: ALL" | sudo tee /etc/sudoers.d/$USER

reference#