Quick check of common Linux commands

This article organizes common commands according to daily Linux usage scenarios. in the example <file>、<directory>、<user>、<pid> Content such as content needs to be replaced with the actual file name, directory, user name or process number.

Common Linux catalogs

View the current environment

View current user name

whoami

View the current directory

pwd

View currently logged in users

who

View more detailed login information

w

View host name

hostname

View system runtime and load

uptime

View Linux kernel version

uname -r

View complete system information

uname -a

View release information

cat /etc/os-release

Check system time

date

browse the directory

View the current directory content

ls

View in detailed format

ls -l

Show Hidden Files

ls -a

Display hidden files and display file size in an easy-to-read manner

ls -lah

Sort by modification time

ls -lt

Sort by file size

ls -lhS

switch directory

Enter the specified directory

cd <directory>

Return to the previous directory

cd ..

Return to user home directory

cd ~

You can also use directly:

cd

Return to the previous directory

cd -

Enter the root directory

cd /

create files and directories

create an empty file

touch <file>

Creating multiple files simultaneously

touch file1.txt file2.txt file3.txt

create a directory

mkdir <directory>

Recursively create a multi-level directory

mkdir -p path/to/directory

Create multiple directories simultaneously

mkdir dir1 dir2 dir3

Copying files and directories

copy files

cp <source> <destination>

Copy the file and rename it

cp source.txt backup.txt

Recursively copy directory

cp -r <source-directory> <destination-directory>

Retain permissions, timestamps and other attributes copying

cp -a <source> <destination>

Prompt before overwriting files

cp -i <source> <destination>

Move and rename files

move files

mv <source> <destination>

rename files

mv old-name.txt new-name.txt

mobile directory

mv <directory> <destination>

Prompt before overwriting target file

mv -i <source> <destination>

delete files and directories

delete files

rm <file>

delete multiple files

rm file1.txt file2.txt

Delete empty directory

rmdir <directory>

Recursively delete directories and their contents

rm -r <directory>

Confirm before deleting

rm -ri <directory>

+++Danger:rm -rf rm -rf Target directories will be recursively and forcibly deleted, will not enter the Recycle Bin, and will not be interrogated one by one.

For example:

rm -rf <directory>

Be especially cautious when using variables or wildcards. You can pass it before implementation ls Check the match results:

ls <target>

Confirm that there is no error before performing the deletion operation. +++

view the file contents

Export entire file

cat <file>

displays line numbers

cat -n <file>

Pagination to view long files

less <file>

in less Middle:

↑ / ↓    上下移动
Space    下一页
b        上一页
/keyword 搜索
n        下一个匹配
q        退出

View the first 10 lines of the file

head <file>

View the first 20 lines of the file

head -n 20 <file>

View the last 10 lines of the file

tail <file>

View the last 50 lines of the file

tail -n 50 <file>

View new content in files in real time

tail -f <file>

Commonly used to view logs:

tail -f /var/log/syslog

edit the file

Editing files with Nano

nano <file>

Common shortcut keys:

Ctrl + O    保存
Ctrl + X    退出
Ctrl + W    搜索

Editing files with Vim

vim <file>

Common operations:

i        进入插入模式
Esc      返回普通模式
:w       保存
:q       退出
:wq      保存并退出
:q!      放弃修改并退出
/word    搜索
dd       删除当前行
yy       复制当前行
p        粘贴
u        撤销

file search

Find by file name

find <directory> -name "<filename>"

For example:

find /etc -name "nginx.conf"

Ignore case lookups

find <directory> -iname "<filename>"

Find the specified extension file

find . -name "*.log"

Find a catalog

find . -type d -name "<directory-name>"

find files

find . -type f -name "<filename>"

Find files that have been modified in the last day

find . -type f -mtime -1

Find files larger than 100 MB

find . -type f -size +100M

Find command location

which <command>

For example:

which python3

Find command, source code and manual locations

whereis <command>

search text

Search for strings in files

grep "<keyword>" <file>

ignore case

grep -i "<keyword>" <file>

Display matching line numbers

grep -n "<keyword>" <file>

Recursive search directory

grep -r "<keyword>" <directory>

Recursively searches and displays line numbers

grep -rn "<keyword>" <directory>

Eliminate matches

grep -v "<keyword>" <file>

Use extended regular expressions

grep -E "<pattern>" <file>

Searching for running processes

ps aux | grep <process-name>

File compression and decompression

Create a tar archive

tar -cvf archive.tar <directory>

Extract tar archives

tar -xvf archive.tar

Create a gzip archive

tar -czvf archive.tar.gz <directory>

Unpack tar.gz

tar -xzvf archive.tar.gz

Create an xz archive

tar -cJvf archive.tar.xz <directory>

Unpack tar.xz

tar -xJvf archive.tar.xz

View the contents of the compressed package but do not decompress it

tar -tvf archive.tar.gz

Extract it to the specified directory

tar -xzvf archive.tar.gz -C <directory>

Create a ZIP archive

zip -r archive.zip <directory>

extracting ZIP

unzip archive.zip

Extract ZIP to the specified directory

unzip archive.zip -d <directory>

file permissions

Linux file permissions are divided into:

r = read    读取
w = write   写入
x = execute 执行

Permission objects are divided into:

u = user    文件所有者
g = group   所属用户组
o = others  其他用户
a = all     所有用户

View file permissions

ls -l <file>

For example:

-rwxr-xr-- 1 qzh qzh 1024 Sep 2 12:00 script.sh

Among them:

rwx    所有者权限
r-x    用户组权限
r--    其他用户权限

Increase execution rights for owners

chmod u+x <file>

Remove write permissions from other users

chmod o-w <file>

Add execution rights for all users

chmod a+x <file>

Use numbers to set permissions

chmod 755 <file>

Digital authority correspondence:

Common permissions:

chmod 644 <file>
chmod 755 <file>
chmod 600 <file>

Among them:

644    普通文本文件常见权限
755    可执行程序或目录常见权限
600    私钥等敏感文件常见权限

recursively modify directory permissions

chmod -R 755 <directory>

Modify file owner

Modify file owner

sudo chown <user> <file>

Modify both owners and user groups

sudo chown <user>:<group> <file>

Recursively modify the directory owner

sudo chown -R <user>:<group> <directory>

Modify the user group to which the file belongs

sudo chgrp <group> <file>

user management

View current user UIDs and user groups

id

View specified user information

id <user>

create user

sudo adduser <user>

delete user

sudo deluser <user>

Delete users and their home directories

sudo deluser --remove-home <user>

Modify the current user password

passwd

Modify the specified user password

sudo passwd <user>

switch user

su - <user>

su to root user

sudo -i

Execute a single command with root privileges

sudo <command>

user group Management

View the user group to which the current user belongs

groups

View the user group to which the specified user belongs

groups <user>

create user groups

sudo groupadd <group>

Add users to user groups

sudo usermod -aG <group> <user>

For example, adding users docker User Group:

sudo usermod -aG docker <user>

Remove users from user groups

sudo gpasswd -d <user> <group>

process management

View the current terminal process

ps

View all processes in the system

ps aux

View processes in tree structure

ps auxf

Dynamic view of system processes

top

if you installed a htop：

htop

Find PID based on process name

pgrep <process-name>

Display both process name and PID

pgrep -a <process-name>

Terminate the specified process

kill <pid>

Force termination of specified process

kill -9 <pid>

Terminate a process based on name

pkill <process-name>

Force process termination based on name

pkill -9 <process-name>

Running tasks in the background

Put the command in the background and run it

<command> &

View the current Shell background tasks

jobs

Switch background tasks to the foreground

fg %1

Continue suspended tasks to run in the background

bg %1

Let the program exit the terminal and continue running

nohup <command> &

For example:

nohup python3 app.py > app.log 2>&1 &

View the daemon PID

echo $!

systemd service management

Modern Ubuntu, Debian, Rocky Linux, CentOS and other distributions are commonly used systemd Manage system services.

Check service status

systemctl status <service>

For example:

systemctl status ssh

start the service

sudo systemctl start <service>

stop service

sudo systemctl stop <service>

restart the service

sudo systemctl restart <service>

Reload service configuration

sudo systemctl reload <service>

Set up service startup

sudo systemctl enable <service>

Start immediately and set up booting

sudo systemctl enable --now <service>

Cancel booting

sudo systemctl disable <service>

Check whether the service is turned on

systemctl is-enabled <service>

Check if the service is running

systemctl is-active <service>

View failed services

systemctl --failed

View systemd logs

view system logs

journalctl

View the specified service log

journalctl -u <service>

View service logs in real time

journalctl -u <service> -f

View the last 100 rows of logs

journalctl -u <service> -n 100

Check the logs since this launch

journalctl -b

View the log of the last boot

journalctl -b -1

View the latest hour's log

journalctl --since "1 hour ago"

View CPU and memory

View CPU information

lscpu

Check the number of CPU cores

nproc

Check memory usage

free -h

Observe memory changes in real time

watch -n 1 free -h

View system load

uptime

You can also use:

cat /proc/loadavg

View disk space

View file system disk usage

df -h

Display file system type also

df -Th

View the file system space where the specified directory is located

df -h <directory>

View the current directory size

du -sh .

View the specified directory size

du -sh <directory>

View the size of each file and directory in the current directory

du -sh *

sorted by size

du -sh * | sort -h

View the top 20 projects in the current catalog

du -ah . | sort -rh | head -n 20

View disks and partitions

View Block Devices

lsblk

Display file system type and UUID

lsblk -f

View disk partition information

sudo fdisk -l

View File System UUID

sudo blkid

Check the current mounting status

findmnt

Mount the file system

Create a mount directory

sudo mkdir -p /mnt/data

Mount partition

sudo mount <device> /mnt/data

For example:

sudo mount /dev/sdb1 /mnt/data

unmount the file system

sudo umount /mnt/data

You can also uninstall through your device:

sudo umount /dev/sdb1

View permanent mount configuration

cat /etc/fstab

sudo cp /etc/fstab /etc/fstab.bak

sudo mount -a

Common LVM commands

View physical volumes

sudo pvs

View Volume Group

sudo vgs

View logical volumes

sudo lvs

View detailed logical volume information

sudo lvdisplay

Allocate all free space in a volume group to logical volumes

sudo lvextend -l +100%FREE <logical-volume>

For example:

sudo lvextend -l +100%FREE /dev/ubuntu-vg/ubuntu-lv

Expand the ext4 file system

sudo resize2fs <logical-volume>

Capacity expansion of XFS file system

sudo xfs_growfs <mount-point>

network information

View network card and IP address

ip addr

Abbreviations:

ip a

View only IPv4 addresses

ip -4 addr

view the routing table

ip route

Abbreviations:

ip r

View default gateway

ip route | grep default

View neighbor and ARP information

ip neigh

View DNS configuration

cat /etc/resolv.conf

using systemd-resolved Can also be used in the system:

resolvectl status

Network connectivity testing

Test whether the target host is reachable

ping <host>

Stop after sending 4 packets

ping -c 4 <host>

View the routes taken to reach the target host

traceroute <host>

if it is not installed traceroute, some systems can use:

tracepath <host>

Query domain name resolution

nslookup <domain>

You can also use:

dig <domain>

Query the specified record

dig <domain> A
dig <domain> AAAA
dig <domain> MX

view the port

Check the TCP and UDP ports you are listening on

ss -tuln

Display the corresponding process at the same time

sudo ss -tulpn

View the specified port

sudo ss -tulpn | grep :<port>

For example, check the 8080 port:

sudo ss -tulpn | grep :8080

View the processes occupying the specified port

sudo lsof -i :<port>

For example:

sudo lsof -i :8080

HTTP request

Get web content

curl <url>

View only response headers

curl -I <url>

Follow HTTP redirection

curl -L <url>

Download the file and keep the original file name

curl -O <url>

Download the file and specify the file name

curl -o <filename> <url>

Send GET request and display details

curl -v <url>

Send POST request

curl -X POST <url>

Send JSON data

curl -X POST \
  -H "Content-Type: application/json" \
  -d '{"name":"test"}' \
  <url>

Download files using wget

download files

wget <url>

Specify the save file name

wget -O <filename> <url>

breakpoint continuous transmission

wget -c <url>

background download

wget -b <url>

SSH remote login

Log in to the remote server

ssh <user>@<host>

Specify the SSH port

ssh -p <port> <user>@<host>

specify a private key

ssh -i <private-key> <user>@<host>

remote command execution

ssh <user>@<host> "<command>"

For example:

ssh qzh@192.168.1.10 "hostname"

SSH key

Create Ed25519 key

ssh-keygen -t ed25519 -C "you@example.com"

Create an RSA key

ssh-keygen -t rsa -b 4096 -C "you@example.com"

Copy the public key to the remote server

ssh-copy-id <user>@<host>

View public key

cat ~/.ssh/id_ed25519.pub

Test SSH configuration

ssh -v <user>@<host>

SCP file transfer

Upload local files to remote server

scp <file> <user>@<host>:<remote-path>

Download files from remote servers

scp <user>@<host>:<remote-file> <local-path>

Recursively upload directory

scp -r <directory> <user>@<host>:<remote-path>

Specify the SSH port

scp -P <port> <file> <user>@<host>:<remote-path>

rsync file synchronization

synchronize directory

rsync -av <source>/ <destination>/

Display synchronization progress

rsync -av --progress <source>/ <destination>/

Sync to remote server via SSH

rsync -av <source>/ <user>@<host>:<destination>/

Sync from remote server to local

rsync -av <user>@<host>:<source>/ <destination>/

Delete unnecessary files on the target side to make both ends completely consistent

rsync -av --delete <source>/ <destination>/

rsync -av --delete --dry-run <source>/ <destination>/

APT package management

Suitable for Ubuntu, Debian and other distributions.

Update software package index

sudo apt update

Upgrade installed software packages

sudo apt upgrade

install software

sudo apt install <package>

Remove software but retain configuration

sudo apt remove <package>

Remove software and its configuration

sudo apt purge <package>

Clean up dependencies that you no longer need

sudo apt autoremove

Search software packages

apt search <keyword>

View package information

apt show <package>

View installed packages

apt list --installed

DNF package management

Suitable for Fedora, Rocky Linux, AlmaLinux and other distributions.

update package

sudo dnf upgrade

install software

sudo dnf install <package>

remove software

sudo dnf remove <package>

Search software packages

dnf search <keyword>

View package information

dnf info <package>

environment variable

View all environment variables

env

View specified environment variables

echo $PATH

Temporarily set environment variables

export NAME=value

For example:

export JAVA_HOME=/usr/lib/jvm/java-17-openjdk-amd64

Add directories to your PATH

export PATH="$PATH:/opt/example/bin"

View the current Shell

echo $SHELL

Reload Bash configuration

source ~/.bashrc

It can also be written as:

. ~/.bashrc

Shell redirection

Write standard output to a file and overwrite the original content

<command> > output.txt

Append standard output to a file

<command> >> output.txt

Write standard errors to file

<command> 2> error.log

Save both standard output and standard errors

<command> > output.log 2>&1

You can also use it in Bash:

<command> &> output.log

discard standard output

<command> > /dev/null

Discard standard output and error output

<command> > /dev/null 2>&1

pipeline

pipeline | The standard output of the previous command is used as the standard input of the subsequent command.

search command output

<command> | grep "<keyword>"

paging view command output

<command> | less

Statistics output rows

<command> | wc -l

Delete duplication after sorting

<command> | sort | uniq

Sort by number

<command> | sort -n

reverse order arrangement

<command> | sort -r

text processing

Count the number of file rows

wc -l <file>

Count the number of words

wc -w <file>

Count the number of bytes

wc -c <file>

Sort file content

sort <file>

Remove adjacent duplicate rows

uniq <file>

usually cooperate sort Use:

sort <file> | uniq

Count the number of duplicate rows

sort <file> | uniq -c

Extract specified column

cut -d '<delimiter>' -f <field> <file>

such as read /etc/passwd User name in:

cut -d ':' -f 1 /etc/passwd

Awk common operations

Output first column

awk '{print $1}' <file>

Output the first and third columns

awk '{print $1, $3}' <file>

specified delimiter

awk -F ':' '{print $1}' /etc/passwd

Filter by condition

awk '$3 > 100 {print $1, $3}' <file>

SED Common operations

Replace the first match

sed 's/old/new/' <file>

Replace all matches in one line

sed 's/old/new/g' <file>

Modify files directly

sed -i 's/old/new/g' <file>

Delete blank lines

sed '/^$/d' <file>

command history

View historical commands

history

View the last 20 orders

history 20

Search history command

history | grep "<keyword>"

Implement the previous order

!!

Execute the historical command of the specified number

!<number>

Clear the current Shell history

history -c

Reverse search history command

In the terminal, press:

Ctrl + R

Enter keywords to search for previously executed commands.

command assistance

View the command manual

man <command>

For example:

man ls

View Command Help

<command> --help

For example:

ls --help

View Shell built-in command help

help <command>

For example:

help cd

View command types

type <command>

alias command alias

View current aliases

alias

Temporarily create alias

alias ll='ls -lah'

delete an alias

unalias ll

Permanently add aliases

Write the alias to:

~/.bashrc

For example:

alias ll='ls -lah'
alias gs='git status'

Then reload:

source ~/.bashrc

Timing task Cron

Edit scheduled tasks for current users

crontab -e

View current user's scheduled tasks

crontab -l

Delete all Cron tasks for current users

crontab -r

Basic Cron format:

分 时 日 月 周 命令
*  *  *  *  *
│  │  │  │  │
│  │  │  │  └── 星期：0-7，0 和 7 都表示星期日
│  │  │  └───── 月份：1-12
│  │  └──────── 日期：1-31
│  └─────────── 小时：0-23
└────────────── 分钟：0-59

Execution of scripts at 2 a.m. every day

0 2 * * * /path/to/script.sh

Executed every 5 minutes

*/5 * * * * /path/to/script.sh

Executed every Monday at 8 a.m

0 8 * * 1 /path/to/script.sh

View recent login history

View user login history

last

View login failure records

sudo lastb

Check the user's last login time

lastlog

View open files

View files opened by the system

sudo lsof

View files opened by the specified process

sudo lsof -p <pid>

View which processes use the specified file

sudo lsof <file>

Check the usage of the specified port

sudo lsof -i :<port>

View hardware information

View PCI devices

lspci

View USB devices

lsusb

View Block Devices

lsblk

View memory hardware information

sudo dmidecode --type memory

View BIOS information

sudo dmidecode --type bios

View the system hardware overview

sudo lshw -short

Shutdown and restart

immediate shut down

sudo shutdown -h now

You can also use:

sudo poweroff

immediately restart

sudo reboot

Shut down in 10 minutes

sudo shutdown -h +10

Shut down at specified time

sudo shutdown -h 23:30

Cancel scheduled shutdown

sudo shutdown -c

Common shortcut keys

Common command combinations

View disk space

df -Th

View the space occupied by each directory and sort it

du -sh * | sort -h

finding large files

find / -type f -size +1G 2>/dev/null

View the processes with the highest memory usage

ps aux --sort=-%mem | head

View the processes that use the most CPU

ps aux --sort=-%cpu | head

Check whether the specified port is occupied

sudo ss -tulpn | grep :<port>

Check whether the specified program is running

pgrep -a <process-name>

View logs in real time

tail -f <log-file>

View the service log of the last 100 lines

journalctl -u <service> -n 100

View service logs in real time

journalctl -u <service> -f

Find a file that contains the specified text

grep -rn "<keyword>" <directory>

View the current server IP address

ip -br addr

View default gateway

ip route | grep default

Check the basics of CPU, memory and disks

lscpu
free -h
df -Th

View disk, partition, and LVM status

lsblk
sudo pvs
sudo vgs
sudo lvs
df -Th

Common troubleshooting processes

When services on the server cannot be accessed normally, you can quickly troubleshoot them in the following order:

flowchart TD
    A[服务无法访问] --> B[检查服务状态]
    B --> C[检查服务日志]
    C --> D[检查进程]
    D --> E[检查监听端口]
    E --> F[检查本机网络]
    F --> G[检查远程连通性]
    G --> H[检查磁盘和内存]

1. Check service status

systemctl status <service>

2. View service logs

journalctl -u <service> -n 100

3. viewing process

pgrep -a <process-name>

4. View listening ports

sudo ss -tulpn

5. Check local IP and routing

ip addr
ip route

6. test network connectivity

ping -c 4 <host>

7. Check system resources

free -h
df -Th
uptime