On Tue, Sep 07, 2004 at 02:48:21PM -0500, Tommy Reynolds wrote:
....
> Accepting a dot as part of the username is a new-ish POSIX change and
> not all parts of Linux are happy with it. AFAIK, useradd(8) has a
> bug in its name validation. Other utilities, such as chown(1),
> should be OK.
Caution:
Chown understands
chown user.group
and
chown user:group
If you have a user first.last and last maps to a group some things can
be confusing. For the most part the match of user is done first and
things work but not exactly as expected.
Limit yourself to chown with a : and if you understand this you should
be fine 99%.
Also pay attention to cap letters as noted in the man page for the
passwd file (man 5 passwd) where
account: the name of the user on the
system. It should not contain capital letters.
Also establish policy limits to the length of a user name. Linux
keeps user IDs as numbers in the guts of the system and converts
names to numbers and numbers to names in a modest list of
places. However if a data base, or other application gets in the game
there is a risk of a string overflow when the string is manipulated in
other contexts.
For a point of history I did see this in an old sunos man page.
#include <limits.h>
LOGNAME_MAX 8 /* max # of characters in a login name */
And in Linux I see:
/usr/include/w3c-libwww/wwwsys.h:#define HT_LOGNAME_MAX 64
/usr/include/bits/posix1_lim.h:#define _POSIX_LOGIN_NAME_MAX 9
/usr/include/bits/local_lim.h:#define LOGIN_NAME_MAX 256
The first.middle.last looks like a 'nice' thing but because '.' is
magic in regular expressions it has been excluded for a long time
in Unix history.
Also watch out for user.tla where the tla might map to some MIME type
that virus software and more might filter. Some executive might want
bill.exe as a user name or the comptroller of the company might want
clinton.com.
My preference is for a shortish simple ID in the passwd file and leave
interesting stuff like first.last as an alias in /etc/aliases.
--
T o m M i t c h e l l
In the USA, be informed, Vote Nov 2004.
