There's a different failure mode which should also be addressed here.
If the admin updated
/etc/group but failed to update
/etc/gshadow (on systems which have this setup), logging out and back in will not actually assign you to the new group.
groups will show you the real, current situation, whereas
id will incorrectly print output which indicates that you are properly a member of the group.
uid=1234(tripleee) gid=1234(tripleee) groups=1234(tripleee),4(adm)
tripleee@vbvntv$ ls -l /var/log/mail.log
-rw-r----- 1 root adm 15728 May 26 14:26 /var/log/mail.log
tripleee@vbvntv$ tail /var/log/mail.log
tail: cannot open `/var/log/mail.log' for reading: Permission denied
I can't use
newgrp because it asks for a password, and I don't have a password, only SSH public key authentication.
The solution would be for the admin to revert the manual edit of
/etc/groups and then do it again with
sudo gpasswd -a tripleee adm; or alternatively, to use
grpconv to merge the changes (which I picked up from http://serverfault.com/a/389719/98333)