Whenever I do:

usermod -G groupname username

.... any existing supplementary group of username, as shown from
/etc/group, gets removed and the new one added.

man usermod says:

-G group
Specify an existing group's integer "ID" "," or  char-
acter  string name. It redefines the user's supplemen-
tary group membership. Duplicates between  group  with
the  -g and
-G options are ignored.  No  more  than  NGROUPS_UMAX
groups may be specified as defined in  <param.h>.


So I assume NGROUPS_UMAX is set to 1 ?


Is it alright then to just directly modify /etc/group so that the
username is in more than one supplementary group ?

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noone <noone@noone.org> wrote in message news:<9zoKb.79333$aT.58320@news-server.bigpond.net.au>...
quote:

> Whenever I do:
>
> 	usermod -G groupname username
>
> .... any existing supplementary group of username, as shown from
> /etc/group, gets removed and the new one added.
>
> So I assume NGROUPS_UMAX is set to 1 ?
>
>
> Is it alright then to just directly modify /etc/group so that the
> username is in more than one supplementary group ?


You did not specify your particular flavor of Unix. However usermod
usually accepts one or more groups for the -G option as in

[ -G group [, group ...]]

and then does a replacement operation i.e. replaces all existing
supplementary groups with the specified supplementary group(s).
It does not incrementally all supplementary groups.

- Finnbarr

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in comp.unix.admin i read:
quote:

>Whenever I do:
>
>	usermod -G groupname username
>
>.... any existing supplementary group of username, as shown from
>/etc/group, gets removed and the new one added.


naturally, exactly as your documentation says will happen ...
quote:

>      -G group
>            Specify an existing group's integer "ID" "," or  char-
>            acter  string name. It redefines the user's supplemen-
>            tary group membership.


i.e., it specifies the group list, replacing whatever is current.
quote:

>Is it alright then to just directly modify /etc/group so that the
>username is in more than one supplementary group ?


that's one way.  be sure you aren't editing the file while others are doing
so, otherwise you'll have a `last writer wins' result, i.e., your changes
may disappear.  your system may have a `vigr' command which performs simple
locking to prevent such from happening.

another way is to enumerate the current list and append the new group so
that usermod can be presented with a list with which i wants to work and
you get the result you want, e.g.,

# usermod -G `id -G $user | tr ' ' ,`,$addgroup $user

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