getut(S)

getut: getutent, getutid, getutline, pututline, setutent, endutent, utmpname -- access utmp file entry

Synopsis

   cc [flag . . . ] file . . . -lgen [library] . . .
   
   #include <utmp.h>
   

   struct utmp getutent (void);
   

   struct utmp getutid (const struct utmp id);
   

   struct utmp getutline (const struct utmp line);
   

   struct utmp pututline (const struct utmp utmp);
   

   void setutent (void);
   

   void endutent (void);
   

   int utmpname (const char file);

Description

getutent, getutid, getutline, and pututline each return a pointer to a utmp structure. [See utmp(F)].

getutent reads in the next entry from a utmp-like file. If the file is not already open, it opens it. If it reaches the end of the file, it fails.

getutid searches forward from the current point in the utmp file until it finds an entry with a ut_type matching id->ut_type if the type specified is RUN_LVL, BOOT_TIME, OLD_TIME, or NEW_TIME. If the type specified in id is INIT_PROCESS, LOGIN_PROCESS, USER_PROCESS, or DEAD_PROCESS, then getutid will return a pointer to the first entry whose type is one of these four and whose ut_id field matches id->ut_id . If the end of file is reached without a match, it fails.

getutline searches forward from the current point in the utmp file until it finds an entry of the type LOGIN_PROCESS or USER_PROCESS that also has a ut_line string matching the line->ut_line string. If the end of file is reached without a match, it fails.

pututline writes out the supplied utmp structure into the 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. It returns a pointer to the utmp structure.

setutent resets the input stream to the beginning of the file. This reset should be done before each search for a new entry if it is desired that the entire file be examined.

endutent closes the currently open file.

utmpname allows the user to change the name of the file examined, from /var/adm/utmp to any other file. It is most often expected that this other file will be /var/adm/wtmp. If the file does not exist, this will not be apparent until the first attempt to reference the file is made. utmpname does not open the file. It just closes the old file if it is currently open and saves the new file name. If the file name given is longer than 79 characters, utmpname returns 0. Otherwise, it will return 1.

Files

/var/adm/utmp
/var/adm/wtmp

Errors

A null pointer is returned upon failure to read, whether for permissions or having reached the end of file, or upon failure to write.

References

getutx(S), ttyslot(S), utmp(F)

Notices

The most current entry is saved in a static structure. Multiple accesses require that it be copied before further accesses are made. On each call to either getutid or getutline, the routine examines 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 area after each success, or getutline would just return the same structure over and over again. There is one exception to the rule about emptying 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 utmp and wtmp files.