Difference between adduser and usermod -G -a

Question

What is the difference between

adduser user_name group_name 

and

usermod -G -a user_name group_name 

At first glance they seems to do the same thing : add a user to a group.

Solution 1

adduser and usermod are two different utilities which have in common the fact that both can add a user to a group.

According to man adduser

adduser is friendlier front ends to the low level tools like useradd, groupadd and usermod programs.

More info:

• man adduser : adduser, addgroup - add a user or group to the system
• man usermod : usermod - modify a user account

Solution 2

At first glance, yes.

At second glance, usermod -G -a user_name group_name is not correct.

The -G option should be followed by the group name(s).

$ sudo usermod -G -a nogroup muru
[sudo] password for muru:
usermod: group '-a' does not exist
$ sudo usermod -a -G muru nogroup
usermod: user 'nogroup' does not exist

The -a can come before -G, or after the group name(s), but not between -G and the group name(s).

As a side note, adduser itself uses gpasswd:

$ grep gpasswd $(which adduser)
    my $gpasswd = &which('gpasswd');
    &systemcall($gpasswd, '-a',$existing_user,$existing_group);

Comments

[snoob dogg]

ok so, the two commands I give do exactly the same thing ?

[Terrance]

@snoobdogg What is meant is that they are different. usermod cannot add a user to the system like adduser can. They just happen to share the ability to add a user to a group.

[snoob dogg]

ok I get it, but the two commands I give in my question do the same thing yes or no?

[Yaron]

@snoobdogg - you can add a user to a group using the two commands as you specify in your question. Those two commands differ in various other parameters.

[Terrance]

@snoobdogg Yes, they are the same commands. From the adduser man page: If called with two non-option arguments, adduser will add an existing user to an existing group.