setuid(2)                 SYSTEM CALLS                  setuid(2)



NAME
     setuid, setgid - set user and group IDs

SYNOPSIS
     #include <sys/types.h>
     #include <unistd.h>

     int setuid(uidt uid);

     int setgid(gidt gid);

DESCRIPTION
     The setuid system call sets the real user ID, effective user
     ID,  and  saved  user ID of the calling process.  The setgid
     system call sets the real group ID, effective group ID,  and
     saved  group  ID of the calling process.  At login time, the
     real user ID, effective user ID, and saved user  ID  of  the
     login  process are set to the login ID of the user responsi-
     ble for the creation of the process.  The same is  true  for
     the  real,  effective,  and saved group IDs; they are set to
     the group ID of the user responsible for the creation of the
     process.   When  a  process  calls exec(2) to execute a file
     (program), the user and/or group identifiers associated with
     the  process  can  change.   If  the file executed is a set-
     user-ID file, the effective and saved user IDs of  the  pro-
     cess are set to the owner of the file executed.  If the file
     executed is a set-group-ID file,  the  effective  and  saved
     group  IDs  of  the process are set to the group of the file
     executed.  If the file executed  is  not  a  set-user-ID  or
     set-group-ID  file,  the  effective  user ID, saved user ID,
     effective group ID, and saved group ID are not changed.  The
     following  subsections  describe  the behavior of setuid and
     setgid with respect to the three types  of  user  and  group
     IDs.

  setuid
     If the effective user ID of the process  calling  setuid  is
     the  superuser,  the real, effective, and saved user IDs are
     set to the uid parameter.  If the effective user ID  of  the
     calling  process is not the superuser, but uid is either the
     real user ID or the saved user ID of  the  calling  process,
     the effective user ID is set to uid.

  setgid
     If the effective user ID of the process  calling  setgid  is
     the  superuser, the real, effective, and saved group IDs are
     set to the gid parameter.  If the effective user ID  of  the
     calling  process is not the superuser, but gid is either the
     real group ID or the saved group ID of the calling  process,
     the  effective  group  ID  is set to gid.  setuid and setgid
     fail if one or more of the following is true:




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setuid(2)                 SYSTEM CALLS                  setuid(2)



     EPERM     For setuid, if the effective user ID  is  not  the
               superuser,  and  the  uid parameter does not match
               either the real or saved user IDs.  For setgid, if
               the  effective  user  ID is not the superuser, and
               the gid parameter does not match either  the  real
               or saved group IDs.

     EINVAL    The uid or gid is out of range.

DIAGNOSTICS
     Upon successful completion, a value of 0 is returned.   Oth-
     erwise,  a value of -1 is returned and errno is set to indi-
     cate the error.

SEE ALSO
     intro(2), exec(2), getgroups(2), getuid(2), stat(5).







































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