linux user management

• 0) check user info   id <username>
• 1)  users / groups are owners of file or directory

bsc@ubuntu:/home$ ls -lt
total 8 
drwxr-xr-x 25 bsc yu 4096 Apr 15 13:27 yu    //  bsc is username, yu is group 
drwxr-xr-x 15 test test 4096 Mar 16 2016 test

users in the same grops can share files/directory 

• 2) Add user and groups 

in ubuntu `useradd` and `adduser` are same functions , but adduser can only be accessed by root user, always user adduser 

groupadd  to add groups

useradd or usermod to change the group of the user

usermod <username> -aG <user_new_group> 

to change user primay group

usermod <username> -g <user new group>

 

• 3) delete user or group

userdel,  groupdel  -r 

 

• 4) groupmod 

-g, --gid GID change the group ID to GID

-n, --new-name NEW_GROUP      change the name to NEW_GROUP

 

• 5) to swtich user : su - <username> 

 

• 6) default useradd cofigure   in /etc/default/useradd

default user perporty in /etc/login.def

 

• 7) change user password : chage <username> or passwd <username>

 

• 8)user configuration file

when a new user created,  the configure saved in /etc/passwd and /etc/shadow 

e.g  bsc:x:1000:1000:bsc:/home/yu:/bin/bash, /username/password/uid/pid/use_describiton/home dir_/user_shell to  change the etc/passwd usevipw.

 

• 9) group  configuration file

adm:x:4:syslog,test,bsc      ;  / group name/group password/group id/ group members 

yu:x:1000:     ; / if the group is primary group, there is no group member in it , just it self