Linux change or rename user name and UID (user-id)

Note: if usermod is not in your path, you can use "whereis" to find it or add the following to your path:“/usr/kerberos/sbin:/usr/kerberos/bin:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin”.

需要注意的一点就是当你改变了某个用户的uid以后，之前由这个用户创建的目录/文件的owner就变成了老的uid，你必须手动找出所有的这些目录/文件，然后chown命令修改它们的owner。

from: http://www.cyberciti.biz/faq/howto-change-rename-user-name-id/

by Vivek Gite on January 4, 2007 · 34 comments

Q. How do I change user name (rename user name) or UID under Linux operating system?

A. Use the usermod command to change user name under Linux. it modifies the system account files to reflect the changes that are specified on the command line.

Syntax is as follows
usermod -l login-name old-name

Where,

=> The name of the user will be changed from old-name to login_name. Nothing else is changed. In particular, the user's home directory name should probably be changed to
reflect the new login name.

usermod -u UID username

Where,
=> The numerical value of the user's ID (UID) . This value must be unique, unless the -o option is used. The value must be non-negative. Values between 0 and 99 are typically reserved for system accounts. Any files which the user owns and which are located in the directory tree rooted at the user's home directory will have the file user ID changed automatically. Files outside of the user's home directory must be altered
manually.

Task: Change username from tom to jerry

Type usermod command as follows:
# id tom
# usermod -l jerry tom
# id jerry
# id tom


Task: Change user tom UID from 5001 to 10000

Type usermod command as follows
# id tom
# usermod -u 10000 tom
# id tom


Read man page of usermod for more information.