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setgid(2)
NAME
  setgid - Sets the group ID

SYNOPSIS
  #include <unistd.h>

  int setgid (
	  gid_t group_id );

  Application developers may want to specify an #include statement for
  <sys/types.h> before the one for <unistd.h> if programs are being developed
  for multiple platforms. The additional #include statement is not required
  on DIGITAL UNIX systems or by ISO or X/Open standards, but may be required
  on other vendors' systems that conform to these standards.

STANDARDS
  Interfaces documented on this reference page conform to industry standards
  as follows:

  setgid():  POSIX.1, XPG4, XPG4-UNIX

  Refer to the standards(5) reference page for more information about
  industry standards and associated tags.

PARAMETERS
  group_id  Specifies the new group ID.

DESCRIPTION
  The setgid() function sets the real group ID, effective group ID, and the
  saved set group ID to the value specified by the group_id parameter.

  If the process does not have superuser privilege, but the group_id
  parameter is equal to the real group ID or the saved set group ID, the
  setgid() function sets the effective group ID to group_id.  The real group
  ID and saved set group ID remain unchanged.

  Any supplementary group IDs of the calling process remain unchanged.

RETURN VALUES
  Upon successful completion, the setgid() function returns 0 (zero).
  Otherwise, the function returns -1 and sets errno to indicate the error.

ERRORS
  The setgid() function sets errno to the specified values for the following
  conditions:

  [EINVAL]  The value of the group_id parameter is invalid.

  [EPERM]   The process does not have superuser privilege and the group_id
	    parameter does not match the real group ID or the saved set group
	    ID.


RELATED INFORMATION
  Functions: exec(2), getgid(2), setuid(2)

  Standards: standards(5)