ps and username size

[Lombard, David N]

On Wed, Jan 09, 2008 at 09:01:44PM +0100, Cristian Ionescu-Idbohrn wrote:
> On Tue, 8 Jan 2008, Cristian Ionescu-Idbohrn wrote:
> 
> > > > The current svn chops of long usernames to 8 chars.  That may create
> > > > confusion if the output from ps is in any way used to identify
> > > > process owners.  Users:
> > > >
> > > >   'longnameA' and 'longnameB' will both be displayed as 'longname'.
> > > >
> > > > Please consider replacing usernames longer than 8 chars with the
> > > > corresponding uids.  That will make them unique in the ps list.
> > >
> > > Good idea.
> >
> > Super.  I made an attempt in a previous sent patch to do just that.
> > It probably just passed unnoticed :(

Just to be sure, this doesn't guarantee unique output.  An integer string
is a perfectly valid username, both on a full distro and bb/uc (just tested
both).  It may be quite demented, but this is legal in /etc/passwd:

  42:...:100:100:user 42:/home/42:/bin/sh
  frederick:...:42:100:some user:/home/frederick:/bin/sh

So, when ps displays "42", which is it?  Here's an example of the proposed
patch w/ ssh logins by "42" and "frederick"

  ~ # ps
    PID  Uid        VSZ Stat Command
      1 root        508 S   init                 
     ...
     87 root        504 S   udhcpc -n -s /sbin/udhcpc.script 
     97 root        528 S   dropbear -j 
    101 root        512 R   -sh 
    106 root        508 S   /bin/sh /sbin/acpid 
    108 root        584 S   dropbear -j 
    109 42          508 S   -sh 
    114 root        584 S   dropbear -j 
    115 42          508 S   -sh 
    121 root        508 R   ps 
  ~ # 

Without the patch, pid 115 is written as:
    115 frederick    508 S   -sh 

As noted, the full procps version creates equally confused output:

  4 S root     27060  2997  0  75   0 -  1105 wait   15:24 pts/4    00:00:00 su - 4242
  4 S 4242     27063 27060  0  83   0 -  1095 -      15:24 pts/4    00:00:00 -bash
  4 S root     27108 27089  0  75   0 -  1106 wait   15:24 pts/5    00:00:00 su - frederick
  4 S 4242     27112 27108  0  85   0 -  1095 -      15:24 pts/5    00:00:00 -bash

Again, this is truly a corner case, and I'm quite happy to argue any confusion
is richly deserved...

-- 
David N. Lombard, Intel, Irvine, CA
I do not speak for Intel Corporation; all comments are strictly my own.