setregid - set real and effective group IDs
#include <unistd.h> int setregid(gid_t rgid, gid_t egid);
The setregid() function is used to set the real and effective group IDs of the calling process. If rgid is −1, the real group ID is not changed; if egid is −1, the effective group ID is not changed. The real and effective group IDs may be set to different values in the same call.
If the {PRIV_PROC_SETID} privilege is asserted in the effective set of the calling process, the real group ID and the effective group ID can be set to any legal value.
If the {PRIV_PROC_SETID} privilege is not asserted in the effective set of the calling process, either the real group ID can be set to the saved set-group-ID from execve(2), or the effective group ID can either be set to the saved set-group-ID or the real group ID.
In either case, if the real group ID is being changed (that is, if rgid is not −1), or the effective group ID is being changed to a value not equal to the real group ID, the saved set-group-ID is set equal to the new effective group ID.
Upon successful completion, 0 is returned. Otherwise, −1 is returned, errno is set to indicate the error, and neither of the group IDs will be changed.
The setregid() function will fail if:
The value of rgid or egid is less than 0 or greater than UID_MAX (defined in <limits.h>).
The {PRIV_PROC_SETID} privilege is not asserted in the effective set of the calling processes and a change was specified other than changing the real group ID to the saved set-group- ID or changing the effective group ID to the real group ID or the saved group ID.
If a set-group-ID process sets its effective group ID to its real group ID, it can still set its effective group ID back to the saved set-group-ID.
See attributes(5) for descriptions of the following attributes:
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execve(2), getgid(2), setreuid(2), setuid(2), attributes(5), privileges(5), standards(5)