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I have written a script to add chrooted sFTP users.

The useradd command is:

sudo useradd -Ng sftponly -ms /bin/false "$USER"

Did it work?

groups $USER
$USER : sftponly

Yes it did. Great!

Then I take a look at /etc/group and there is no $USER in sftponly. I try logging in and out (shouldn't need to - I am not $USER) and nothing changes. (for $USER == yoko):

ftp:x:114:
sftponly:x:1003:george,john,paul,ringo
incron:x:115:

Why am I seeing $USER in the correct group when using groups, but not in /etc/group?

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2 Answers 2

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You shall not use useradd, but use adduser instead. However, if you insist on using useradd, here is what you should do:

sudo useradd -Ng sftponly -G sftponly -ms /bin/false "$USER"

The -g option only changes the /etc/passwd file, making "sftponly" the primary (login) group ID of the user. The -G option modifies /etc/groups.

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    Isn't this redundant? I mean, is the user not also treated as member of the login-group set in /etc/passwd, even if he isn't listed in /etc/groups?
    – soulsource
    Jul 8, 2013 at 19:17
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    To be frank, good question. I'm not sure, i.e. I'm not sure whether there isn't any program that consults only /etc/group but not /etc/passwd. I think I will ask that on superuser.
    – January
    Jul 8, 2013 at 19:21
  • Yeah - I understand now why they don't appear in /etc/groups but surely having all the information in one canonical spot makes more sense?
    – datakid
    Jul 10, 2013 at 6:43
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From the useradd manpage:

-g, --gid GROUP
    The group name or number of the user's initial login group.

The user's initial login group is the one at the fourth field in a line of the /etc/passwd file. If you look for "yoko" in /etc/passwd you'll find something like:

yoko:x:<yoko's UID>:1003::<yoko's home>:/bin/false

where 1003 is the GID of sftponly group.

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