Linux commands (user management, group and time management)

• User Management   

• Linux system is a multi-user system
• Users are divided into three categories: superuser (root) user id is 0 pseudo user id of the user 1 ---- 499 while there, but not by ordinary users login user id pseudo 500 --- 60000.
• Location of the user information stored in: / ect / passwd file to view the information cat / etc / passwd
• The syntax for creating a user: useradd -u user id -g hostname -c -G users of other user group name description (alias) User Name
•  useradd -u 666 -g root -G sys,users,admin -c 'newUser' uqy97a
• View user belongs syntax group uq97a
• View user syntax cat / etc / passwd
• Simple way to create user syntax useradd username
• User password passwd user name syntax
• Change the name before the name to modify the user login name syntax usermod -l modification
• Delete users (already logged in user can not be deleted)
• userdel -r username name
• Switch user su username name (root user switching without a password)

• User group management

• Linux there is more than one group
• Group information stored in the location / etc / group
• View the document cat etc / goup
• Add a group
• group username name
• Delete Group
• groupdel username name

• time

• View the current time date
• Modified date MMDDHHMMYYYY (month, day, hour, minute, year)
•                              date -s 'yyy-mm-dd HH: MI: SS' (year, month, day, hour, minute, second)
• Change the time zone
• cp /etc/share/zoninfo/Asia/Shanghai  /etc/localtime
• Use network synchronization current time
• ntpdate pool.ntp.org
• View the current system ntpd service is turned on
• service      ntpd   status
• Set boot time                   chkconfig ntpd on    

• sudo usage

• sudo command to elevate certain non-root user privileges:
• With root inputs vim / etc / sudoers file commands the root ALL = (ALL) ALL line copy user root to the regular user to save
• Switch to the ordinary user input back sudo sudo poweroff shutdown operation command you want to operate