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I've seen various Linux file permissions such as rwx and rws, but I have never seen the permission set rwS. Can someone please explain to me what the capitol 'S' stands for?

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up vote 10 down vote accepted

The capital S indicates the file has a setuid bit set but is not executable.

[root@host:/]$ touch file
[root@host:/]$ chmod 4755 file
[root@host:/]$ ls -l file
-rwsr-xr-x 1 root root 0 Jul 25 15:05 file
[root@host:/]$ chmod -x file
[root@host:/]$ ls -l file
-rwSr--r-- 1 root root 0 Jul 25 15:05 file
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From info ls "What information is listed":

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