mail to all users on a system (from root)

Matthew Seaman m.seaman at
Mon Apr 14 02:16:52 PDT 2003

On Sun, Apr 13, 2003 at 09:49:57AM -0500, Mike Meyer wrote:
> In <20030413142842.GB25131 at happy-idiot-talk.infracaninophi>, Matthew Seaman <m.seaman at> typed:
> > On Sun, Apr 13, 2003 at 02:32:35PM +0200, Aslak Evang wrote:
> > > I've searched for ways for root to email all users on a system. The only
> > > easy solution I found included making a shellscript and setting it as an
> > > alias for "everybody". Problem was that in the script you had to insert
> > > all your users manually.
> > > Does anybody know of other methods for sending announcements to all
> > > users on a system? Could have done it with MOTD but few of them actually
> > > log-in. Most just read mail.
> > 
> > Try the attached script which I just slung together.  To use, save the
> > script into a defined place on your HD, say /usr/local/sbin/everybody,
> > and then set up an alias:
> > 
> >     everybody:	"| /usr/local/sbin/everybody"
> > 
> > This script will resend the message to all users with an account on
> > the system -- I've assumed that real people have UIDs over 1000 and
> > system accounts have UIDs less than that.  Note that this is just a
> > quick hack and could be vastly improved --- certainly made much more
> > efficient --- with a little effort.  Only minimally tested: use very
> > cautiously.
> The script is a nice effort, but has a serious efficiency problem -
> it's going to fork a sendmail for every user on the system. For small
> numbers of users, that's acceptable. The attached everybody script
> will connect to the SMTP server on the local system and send just one
> copy of the message, allowing the SMTP server to deal with making
> multiple copies to send to everyone. The downside of this script is
> that it's going to keep the list uf usernames in memory, which will
> eventually cause problems - but not before you've reached numbers that
> would make spammers notice.
> 	<mike
> #!/usr/bin/env python
> "Forward email to everybody on the system."
> import sys, os, pwd, smtplib
> users = [pwd[0] for pwd in pwd.getpwall() if pwd[2] > 1000 and pwd[0] != 'nobody']
> mailer = smtplib.SMTP('localhost')
> mailer.sendmail(os.environ['USER'], users,

Yeah.  Like I said.  If you've got a significant number of users (more
than about 20 say) and there's quite a bit of use of the 'everybody@'
alias, then it's going to be far more efficient just to extract the
list of users from the password database, using something like this
script but written in whatever your favourite language happens to be:

    #!/usr/bin/perl -w
    use User::pwent qw{:FIELDS};
    # Take an E-mail message on stdin and forward it to all users on the
    # system.  Assumes that real users have UIDs >= 1000 and that system
    # accounts do not (other than the nobody account, of course).
        while ( getpwent() ) {
            next if ( $pw_uid < 1000 || $pw_name eq 'nobody' );
            print "$pw_name\n";

Run that on a regular basis --- say every few hours during the day via
a cron job:

    3  9,11,13,15,17 * * *   /usr/local/bin/everybody > /etc/mail/everybody.list

and set up an alias that includes that list in /etc/mail/aliases:

    everybody:	:include: /etc/mail/everybody.list

Nb. using an external file means that you don't need to run
newaliases(1) every time the list of user names changes.  The
'everybody' script I wrote yesterday is, I will freely admit, a hack.
Cute, in some ways, but not production quality.  What can I say?
Writing it certainly beat cleaning the kitchen floor, which is what I
*should* have been doing...



Dr Matthew J Seaman MA, D.Phil.                       26 The Paddocks
                                                      Savill Way
PGP:         Marlow
Tel: +44 1628 476614                                  Bucks., SL7 1TH UK
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