GETLOGIN(2) System Calls Manual GETLOGIN(2)

getlogin, setlogin — get/set login name

#include <unistd.h>

char *
getlogin(void);

int
setlogin(const char *name);

The () routine returns the login name of the user associated with the current session, as previously set by setlogin(). The name is normally associated with a login shell at the time a session is created, and is inherited by all processes descended from the login shell. (This is true even if some of those processes assume another user ID, for example when su(1) is used.)

() sets the login name of the user associated with the current session to name. This call is restricted to the super-user, and is normally used only when a new session is being created on behalf of the named user (for example, at login time, or when a remote shell is invoked).

If a call to getlogin() succeeds, it returns a pointer to a null-terminated string in a static buffer. If the name has not been set, it returns NULL. If a call to setlogin() succeeds, a value of 0 is returned. If setlogin() fails, a value of -1 is returned and an error code is placed in the global location errno.

The following errors may be returned by these calls:

[]
The name parameter gave an invalid address.
[]
The name parameter pointed to a string that was too long. Login names are limited to MAXLOGNAME (from ⟨sys/param.h⟩) characters, currently 12.
[]
The caller tried to set the login name and was not the super-user.

setsid(2)

Login names are limited in length by setlogin(). However, lower limits are placed on login names elsewhere in the system (UT_NAMESIZE in ⟨utmp.h⟩).

In earlier versions of the system, getlogin() failed unless the process was associated with a login terminal. The current implementation (using setlogin()) allows getlogin to succeed even when the process has no controlling terminal. In earlier versions of the system, the value returned by getlogin() could not be trusted without checking the user ID. Portable programs should probably still make this check.

The getlogin() function first appeared in 4.4BSD.

June 9, 1993 BSD 4.2