What are the disadvantages of having a dot in a user name?
POSIX states this about usernames:
[...] To be portable across systems conforming to IEEE Std 1003.1-2001, the value is composed of characters from the portable filename character set. The hyphen should not be used as the first character of a portable user name.
... where the portable filename character set is:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
a b c d e f g h i j k l m n o p q r s t u v w x y z
0 1 2 3 4 5 6 7 8 9 . _ -
Also, the manpage for the /etc/adduser.conf
file states:
VALID NAMES
adduser and addgroup enforce conformity to IEEE Std 1003.1-2001,
which allows only the following characters to appear in group
and user names: letters, digits, underscores, periods, at signs
(@) and dashes. The name may not start with a dash. The "$" sign
is allowed at the end of usernames (to conform to samba).
An additional check can be adjusted via the configuration
parameter NAME_REGEX to enforce a local policy.
However,
Whilst both specifications seem to include the dot, Ubuntu (on my 13.04 at least) seems to disallow it:
⊳ sudo adduser as.df
adduser: Please enter a username matching the regular expression configured
via the NAME_REGEX[_SYSTEM] configuration variable. Use the `--force-badname'
option to relax this check or reconfigure NAME_REGEX.
The default NAME_REGEX
in Ubuntu is (from the /etc/adduser.conf
manpage):
^[a-z][-a-z0-9]*$
- Starting with a lowercase letter then any number of dashes, lowercase letters or digits. No
_
,@
or.
.
So,
in conclusion a dot .
may be used for a Ubuntu username, the NAME_REGEX
just has to be changed in /etc/adduser.conf
. Seeing as it conforms to POSIX, there shouldn't be any problems with having a .
in the username with any POSIX-compliant program.
To enable a dot in usernames
Run this command in a terminal:
sudo nano /etc/adduser.conf
Locate this line (near the end of the file)
#NAME_REGEX="^[a-z][-a-z0-9]*$"
and replace it with
NAME_REGEX='^[a-z][-.a-z0-9]*$'
Note that the
-
must remain the first character in the bracket expression[...]
, otherwise it is treated as specifying a rangea-z
.Press Ctrl+X, then Y, then Enter.
References:
- Why are underscores not allowed in usernames in some distros (Debian for example)
man adduser.conf
Marc Haber explains a possible downside in Debian bug #604242 (Allow dots in username by default):
Having dots in the user name creates some issues with scipts using
chown
, which still accepts dots as separator between user name and group name. Ifchown
still accepts dots, there will be scripts using this notation, which will break if a user name contains a dot.I would recommend keeping the current default (which can be overwritten by local configuration) until
chown
has stopped accepting dots as separator.
And chown
still accepts the dot as separator, although it isn't documented anymore. I agree POSIX compatibility should prevail, and I indeed employ user names containing dots on several systems without any adverse effects.
Applications that reads usernames might use a regex that assumes your username follows the rules and therefore can't handle your username.