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GETLOGIN(2)		 DragonFly System Calls Manual		   GETLOGIN(2)


getlogin, getlogin_r, setlogin -- get/set login name


Standard C Library (libc, -lc)


#include <unistd.h> char * getlogin(void); #include <sys/param.h> int getlogin_r(char *name, int len); int setlogin(const char *name);


The getlogin() routine returns the login name of the user associated with the current session, as previously set by setlogin(). The name is nor- mally 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). getlogin_r() provides the same service as getlogin() except the caller must provide the buffer name with length len bytes to hold the result. The buffer should be at least MAXLOGNAME bytes in length. Setlogin() sets the login name of the user associated with the current session to name. This call is restricted to the super-user, and is nor- mally 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). NOTE: There is only one login name per session. It is CRITICALLY important to ensure that setlogin() is only ever called after the process has taken adequate steps to ensure that it is detached from its parent's session. Making a setsid() system call is the ONLY way to do this. The daemon() library call calls setsid() which is an ideal way of detaching from a controlling terminal and forking into the back- ground. In particular, doing a ioctl(ttyfd, TIOCNOTTY, ...) or setpgrp(...) is NOT sufficient. Once a parent process does a setsid() call, it is acceptable for some child of that process to then do a setlogin() even though it is not the session leader, but beware that ALL processes in the session will change their login name at the same time, even the parent. This is not the same as the traditional UNIX behavior of inheriting priv- ilege. Since the setlogin() system call is restricted to the super-user, it is assumed that (like all other privileged programs) the programmer has taken adequate precautions to prevent security violations.


If a call to getlogin() succeeds, it returns a pointer to a null-termi- nated string in a static buffer, or NULL if the name has not been set. getlogin_r() returns zero if successful, or the error number upon fail- ure. The setlogin() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.


The following errors may be returned by these calls: [EFAULT] The name parameter gave an invalid address. [EINVAL] The name parameter pointed to a string that was too long. Login names are limited to MAXLOGNAME (from <sys/param.h>) characters, currently 17 including null. [EPERM] The caller tried to set the login name and was not the super-user. [ERANGE] The size of the buffer is smaller than the result to be returned.


setsid(2), daemon(3)


getlogin() and getlogin_r() conform to ISO/IEC 9945-1:1996 (``POSIX.1'').


The getlogin() function first appeared in 4.4BSD. The return value of getlogin_r() was changed from earlier versions of FreeBSD to be confor- mant with ISO/IEC 9945-1:1996 (``POSIX.1'').


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 con- trolling terminal. In earlier versions of the system, the value returned by getlogin() could not be trusted without checking the user ID. Porta- ble programs should probably still make this check. DragonFly 5.1 June 9, 1993 DragonFly 5.1

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