查看命令类型:	type 'cmd' 

cat /etc/os-release

修改hostname:  hostnamectl set-hostname 

npm install -g tldr 
或者
pip install tldr

cd /usr/bin
sudo ln -s /home/lyhistory/.local/bin/tldr tldr (/usr/bin/tldr)
或者修改.bashrc
export PATH=$PATH:$HOME/.local/bin

查看用户：
id username
W
Whoami
groups
vim /etc/passwd
cut -d: -f1 /etc/passwd

用户组：
groups username
less /etc/group
groupadd groupname
groupdel groupname
su username #切换用户 
添加新用户： 
useradd username
passwd username
usermod -g groupname username -d /home/test
useradd -g groupname username -d /home/test （注意，最好用home目录，之前碰到过一个问题：用其他系统盘或数据盘，其他人更改了文件夹权限，造成.ssh/id_rsa权限过大，不满足系统安全要求，造成passwordless login失败）
userdel username
gpasswd -d groupname username

/etc/sudoers
visudo

---------------------------------------------------------------------------------------
--- ubuntu
---------------------------------------------------------------------------------------
Enable SUDO:
	By default sudo is not installed on Debian, but you can install it. First enable su-mode:
	You can use sudo -i which will ask for your password. You need to be in the sudoers group for that or have an entry in the /etc/sudoers file.
	Another way is the command su - which will ask for the password of root, but accomplish the same.
	su -
	apt-get install sudo -y
	
    usermod -aG sudo yourusername
    Make sure your sudoers file have sudo group added. Run:
    visudo to modify sudoers file and add following line into it (if it is missing):

    # Allow members of group sudo to execute any command
    %sudo   ALL=(ALL:ALL) ALL
    OR
    chmod u+w /etc/sudoers
    username ALL=(ALL) ALL
    chmod u-w /etc/sudoers

adduser username 
sudo passwd USERNAME
sudo usermod -aG sudo username
su - username
exit;
sudo useradd test -s /bin/bash -m
usermod -aG docker peter


---------------------------------------------------------------------------------------
--- centos
---------------------------------------------------------------------------------------
Enable SUDO:
    By default, on CentOS, members of the wheel group have sudo privileges.
    https://support.hostway.com/hc/en-us/articles/115001509750-How-To-Install-and-Configure-Sudo

useradd -s /bin/bash -m -G wheel username
sudo usermod -aG wheel username
Wheel group https://www.centos.org/forums/viewtopic.php?t=63386


ssh-keygen 
or
ssh-keygen -t rsa

chmod 400 id_rsa

ssh-copy-id username@serveripOrhostname
or 
ssh-copy-id -i ~/.ssh/id_rsa.pub username@serveripOrhostname

scp ~/.ssh/id_rsa grs@adp116:~/.ssh

ssh-keygen -R ip/hostname

多行变成一行，逗号隔开（去掉最后一个逗号）
tr '\n' ',' < input.txt | sed 's/,$/\n/'


cut -f 1 -d: /etc/passwd | xargs -n 1 -I {} bash -c " echo -e '\n{}' ; chage -l {}"

for readonly file:
:w !sudo tee %

scp -rp src/. user@server:dest/

创建文件夹
install -d /path/to/targetfolder

find . -size +1G -ls | sort -k7n

find / -type f -name "mysql-connector-java-5.1.24.jar" -print

find / -type f -name "Locations.xml" -print

//kafka/logs下面有很多日志，格式为：[server|controller].log.YYYY-MM-DD-0X，如果想大概知道有哪几类文件，可以：
find . -type f -maxdepth 1 -exec basename "{}" \; | cut -d'.' -f1 | sort -u

find zookeeper/ -group root

find ./* -type f -follow -name \*.log -daystart -mtime +1 -print0 | xargs -0 rm

find and delete::
https://unix.stackexchange.com/questions/167823/finds-exec-rm-vs-delete
find / -name ".DS_Store" -exec rm {} \;
find / -name .DS_Store -delete
A common method for avoiding the overhead of spawning an external process for each matched file is:
find / -name .DS_Store -print0 | xargs -0 rm
DO NOT do this: find / -delete -name .DS_Store

grep/zgrep "pattern" file/file.gz

grep -r -l "eth[0-9]" /var/log/ #file name only
grep -r -H "eth[0-9]" /var/log/ #print each match and filename

grep -H -r "syscript" ~ | cut -d: -f1 | sort -u

grep -H -r "create_db.sh" ~ | cut -d: -f1 | sort -u

grep -H -r "/apps/lib" ~ | cut -d: -f1 | sort -u


cat Syslog.log | iconv -f GBK -t UTF-8|grep -ai "SEARCH TEXT"

grep -rl oldtext . | xargs sed -i 's/oldtext/newtext/g'

split -a 4 -d -l 20000 2021-02-15_test.log ./test/test_

sed -i 's/#*port = .*/port = 5432/' /postgres/data/postgresql.conf

df -h
du -sh ./*

ls | grep -xv "except this file.txt" | xargs rm -rf

[email protected]
00 15 * * *  echo "Just testing if crond sends email"

# chage -l test
# chage -M 99999 test

~/.bashrc:
export HISTTIMEFORMAT="%d/%m/%y %H:%M "

for i in {1..N}; do history -d START_NUM; done

#Delete your Linux history without leaving a trace!
history -d $((HISTCMD-1)) && history -d [line entry number]