issetugid - determine if current executable is running setuid or setgid


#include <unistd.h>

int issetugid(void);


The issetugid() function enables library functions (in libtermlib, libc,
or other libraries) to guarantee safe behavior when used in setuid or
setgid programs or programs that run with more privileges after a
successful exec(2). Some library functions might be passed insufficient
information and not know whether the current program was started setuid
or setgid because a higher level calling code might have made changes to
the uid, euid, gid, or egid. These low-level library functions are
therefore unable to determine if they are being run with elevated or
normal privileges.

The issetugid() function should be used to determine if a path name
returned from a getenv(3C) call can be used safely to open the specified
file. It is often not safe to open such a file because the status of the
effective uid is not known.

The result of a call to issetugid() is unaffected by calls to setuid(),
setgid(), or other such calls. In case of a call to fork(2), the child
process inherits the same status.

The status of issetugid() is affected only by execve() (see exec(2)). If
a child process executes a new executable file, a new issetugid() status
will be based on the existing process's uid, euid, gid, and egid
permissions and on the modes of the executable file. If the new
executable file modes are setuid or setgid, or if the existing process is
executing the new image with uid != euid or gid != egid, or if the
permitted set before the call to the exec function is not a superset of
the inheritable set at that time, issetugid() returns 1 in the new


The issetugid() function returns 1 if the process was made setuid or
setgid as the result of the last or a previous call to execve().
Otherwise it returns 0.


The issetugid() function is always successful. No return value is
reserved to indicate an error.


See attributes(5) for descriptions of the following attributes:

|Interface Stability | Evolving |
|MT-Level | Async-Signal-Safe |


exec(2), fork(2), setuid(2), getenv(3C), attributes(5), privileges(5)

April 9, 2016 ISSETUGID(2)