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In Linux, how can I identify if a binary file is set-user-ID?

Can I use ls -l?

closed as unclear what you're asking by jasonwryan, Archemar, Stephen Kitt, Anthon, John WH Smith Mar 26 '15 at 11:25

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  • What is the problem with ls -l? – michas Mar 26 '15 at 8:03
  • @michas I meant using ls -l? – Zhenxiao Hao Mar 26 '15 at 8:05
  • Sure you can use ls -l, why the doubt? – michas Mar 26 '15 at 8:09
  • @michas I was not sure. – Zhenxiao Hao Mar 26 '15 at 8:10
2

executing ls -l you will get something like:

-rwSr--r--   1 user user    8111573 Sep 26  2012 net-snmp.tar

where the S (can be also s) indicate this file have SUID set

S is set when you do not have execution flag set

s is set when you have execution flag set

  • 1
    In short: s = x + setuid, S = setuid without x. (setuid+x gets the more "normal" character because it's more common) – immibis Mar 26 '15 at 8:05
3

Either manually look at the file with ls -l filename, or from a script you can use

[ -u filename ] && echo SUID-bit is set

See also man bash:

   -u file
          True  if  file  exists  and its set-user-id bit is set.

See also info ls:

 The file mode bits listed are similar to symbolic mode
 specifications (*note Symbolic Modes::).  But ‘ls’ combines
 multiple bits into the third character of each set of permissions
 as follows:

 ‘s’
      If the set-user-ID or set-group-ID bit and the corresponding
      executable bit are both set.

 ‘S’
      If the set-user-ID or set-group-ID bit is set but the
      corresponding executable bit is not set.

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