Cheatsheet

useradd

sudo useradd <$name> -m -r -s /bin/bash -p <$password>
add as soduer
echo '<$name> ALL=(ALL) NOPASSWD: ALL' >> /etc/sudoers

telnet

a command line interface for communication with a remote device or serve

telnet <$ip> <$port>
for example
telnet 172.27.253.50 9000 #test application connectivity

lsof (list as open files)

everything is a file

lsof <$option:value>
for example

-a List processes that have open files

-c <process_name> List files opened by the specified process

-g List GID number process details

-d <file_number> List the processes occupying this file number

-d List open files in a directory

-D Recursively list open files in a directory

-n List files using NFS

-i List eligible processes. (protocol, :port, @ip)

-p List files opened by the specified process ID

-u List UID number process details

lsof -i:30443 # find port 30443 
lsof -i -P -n # list all connections

awk (Aho, Weinberger, and Kernighan [Names])

awk is a scripting language used for manipulating data and generating reports.

# awk [params] 'script' 
awk <$params> <$string_content>
for example

filter bigger than 3

echo -e "1\n2\n3\n4\n5\n" | awk '$1>3'

func1 func1

ss (socket statistics)

view detailed information about your system’s network connections, including TCP/IP, UDP, and Unix domain sockets

ss [options]
for example
OptionsDescription
-tDisplay TCP sockets
-lDisplay listening sockets
-nShow numerical addresses instead of resolving
-aDisplay all sockets (listening and non-listening)
#show all listening TCP connection
ss -tln
#show all established TCP connections
ss -tan

clean files 3 days ago

find /aaa/bbb/ccc/*.gz -mtime +3 -exec rm {} \;

ssh without affect $HOME/.ssh/known_hosts

ssh -o "UserKnownHostsFile /dev/null" root@aaa.domain.com
ssh -o "UserKnownHostsFile /dev/null" -o "StrictHostKeyChecking=no" root@aaa.domain.com

sync clock

[yum|dnf] install -y chrony \
    && systemctl enable chronyd \
    && (systemctl is-active chronyd || systemctl start chronyd) \
    && chronyc sources \
    && chronyc tracking \
    && timedatectl set-timezone 'Asia/Shanghai'

set hostname

hostnamectl set-hostname develop

add remote key to other server

ssh -o "UserKnownHostsFile /dev/null" \
    root@aaa.bbb.ccc \
    "mkdir -p /root/.ssh && chmod 700 /root/.ssh && echo '$SOME_PUBLIC_KEY' \
    >> /root/.ssh/authorized_keys && chmod 600 /root/.ssh/authorized_keys"
for example
ssh -o "UserKnownHostsFile /dev/null" \
    root@17.27.253.67 \
    "mkdir -p /root/.ssh && chmod 700 /root/.ssh && echo 'ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABgQC00JLKF/Cd//rJcdIVGCX3ePo89KAgEccvJe4TEHs5pI5FSxs/7/JfQKZ+by2puC3IT88bo/d7nStw9PR3BXgqFXaBCknNBpSLWBIuvfBF+bcL+jGnQYo2kPjrO+2186C5zKGuPRi9sxLI5AkamGB39L5SGqwe5bbKq2x/8OjUP25AlTd99XsNjEY2uxNVClHysExVad/ZAcl0UVzG5xmllusXCsZVz9HlPExqB6K1sfMYWvLVgSCChx6nUfgg/NZrn/kQG26X0WdtXVM2aXpbAtBioML4rWidsByDb131NqYpJF7f+x3+I5pQ66Qpc72FW1G4mUiWWiGhF9tL8V9o1AY96Rqz0AVaxAQrBEuyCWKrXbA97HeC3Xp57Luvlv9TqUd8CIJYq+QTL0hlIDrzK9rJsg34FRAvf9sh8K2w/T/gC9UnRjRXgkPUgKldq35Y6Z9wP6KY45gCXka1PU4nVqb6wicO+RHcZ5E4sreUwqfTypt5nTOgW2/p8iFhdN8= Administrator@AARON-X1-8TH' \
    >> /root/.ssh/authorized_keys && chmod 600 /root/.ssh/authorized_keys"

set -x

This will print each command to the standard error before executing it, which is useful for debugging scripts.

set -x

set -e

Exit immediately if a command exits with a non-zero status.

set -x

sed (Stream Editor)

sed <$option> <$file_path>
for example

replace unix -> linux

echo "linux is great os. unix is opensource. unix is free os." | sed 's/unix/linux/'

or you can check https://www.geeksforgeeks.org/sed-command-in-linux-unix-with-examples/

fdisk

list all disk

fdisk -l

create CFS file system

Use mkfs.xfs command to create xfs file system and internal log on the same disk, example is shown below:

mkfs.xfs <$path>

modprobe

program to add and remove modules from the Linux Kernel

modprobe nfs && modprobe nfsd

disown

disown command in Linux is used to remove jobs from the job table.

disown [options] jobID1 jobID2 ... jobIDN
for example

for example, there is a job running in the background

ping google.com > /dev/null &

using jobs - to list all running jobs

jobs -l

using disown -a remove all jobs from the job tables

disown -a

using disown %2 to remove the #2 job

disown %2

generate SSH key

ssh-keygen -t rsa -b 4096 -C "aaron19940628@gmail.com"
sudo ln -sf <$install_path>/bin/* /usr/local/bin

append dir into $PATH (temporary)

export PATH="/root/bin:$PATH"

copy public key to ECS

ssh-copy-id -i ~/.ssh/id_rsa.pub root@10.200.60.53

echo “nameserver 8.8.8.8” | sudo tee /etc/resolv.conf echo “nameserver 8.8.4.4” | sudo tee -a /etc/resolv.conf