edit file
vi aaa.txt Open aaa.txt file The esc key toggles between edit and command modes In the command mode, enter: (colon), you can enter the command :s/ string1/string2 Replace string1 with string2 :wq! to save the file and exit :q! Force quit file editing
check the file
cat aaa.txt View the content of the aaa.txt file head -5 aaa.txt View the contents of the first 5 lines of the aaa.txt file tail -10 aaa.txt displays the last 10 lines of the aaa.txt file
Operating users and user groups
su root switch to root user whoami View currently logged in users groups View the group to which the current user belongs id View current user UID and GID useradd adds a new user (under root) passwd sa Set the password of the sa user (under root) passwd change password userdel delete user (under root)
groupadd g1 Add g1 group (under root) usermod -g g1 sa assign the sa user to the g1 group (under root)
Set file permissions
chmod 751 temp set 751 permissions to temp folder -rwxr-x--x 111 101 001 751
Abbreviation for ps Process Status, used to display the status of the current process