getut(3)
NAME
getutent, getutid, getutline, pututline, setutent, endutent, utmpname − access utmp file entry
SYNTAX
#include <utmp.h>
struct utmp *getutent()
struct utmp *getutid(id)
struct utmp *id;
struct utmp *getutline(line)
struct utmp *line;
void pututline(utmp)
struct utmp *utmp;
void setutent()
void endutent()
void utmpname(file)
char *file;
DESCRIPTION
The getutent, getutid and getutline subroutines each return a pointer to a structure of the following type:
struct utmp {
char ut_user[8] ; /∗ User login name ∗/
char ut_id[4] ; /∗ for SYSTEM V compatibility ∗/
char ut_line[12] ; /∗ device name (console, ttynn) ∗/
char ut_host[16] ; /∗ host name, if remote ∗/
short ut_pid ; /∗ process id ∗/
short ut_type ; /∗ type of entry ∗/
struct exit_status {
short e_termination ; /∗ Process termination status ∗/
short e_exit ; /∗ Process exit status ∗/
} ut_exit ; /∗ Exit status of a process
∗ marked DEAD_PROCESS. ∗/
time_t ut_time ; /∗ time entry was made ∗/
};
The getutent subroutine reads in the next entry from a /etc/utmp -like file. If the file is not already open, it opens it. If it reaches the end of the file, it fails.
The getutline subroutine searches forward from the current point in the /etc/utmp file until it finds an entry which has a ut_line string matching the line−>ut_line string. If the end of file is reached without a match, it fails.
The pututline writes out the supplied structure utmp into the /etc/utmp file. It uses getutid to search forward for the proper place if it finds that it is not already at the proper place. It is expected that normally the user of pututline will have searched for the proper entry using one of the getut routines. If so, pututline will not search. If pututline does not find a matching slot for the new entry, it will add a new entry to the end of the file.
The setutent subroutine resets the input stream to the beginning of the file. This should be done before each search for a new entry if it is desired that the entire file be examined.
The endutent closes the currently open file.
The utmpname allows the user to change the name of the file examined, from /etc/utmp to any other file. It is most often expected that this other file will be /usr/adm/wtmp. If the file does not exist, this will not be apparent until the first attempt to reference the file is made. The utmpname does not open the file. It just closes the old file if it is currently open and saves the new file name.
COMMENTS
The most current entry is saved in a static structure. Multiple accesses require that it be copied before further accesses are made. Each call to either getutid or getutline sees the routine examine the static structure before performing more I/O. If the contents of the static structure match what it is searching for, it looks no further. For this reason to use getutline to search for multiple occurrences, it would be necessary to zero out the static after each success, or getutline would just return the same pointer over and over again. There is one exception to the rule about removing the structure before further reads are done. The implicit read done by pututline (if it finds that it is not already at the correct place in the file) will not hurt the contents of the static structure returned by the getutent, getutid or getutline routines, if the user has just modified those contents and passed the pointer back to pututline.
These routines use buffered standard I/O for input, but pututline uses an unbuffered non-standard write to avoid race conditions between processes trying to modify the /etc/utmp and /usr/adm/wtmp files.
DIAGNOSTICS
A NULL pointer is returned upon failure to read, whether for permissions or having reached the end of file, or upon failure to write.
FILES
/etc/utmp
/usr/adm/wtmp