Originální popis anglicky:
getutent, getutid, getutline, pututline, setutent, endutent, utmpname - access
utmp file entries
Návod, kniha: Library functions
#include <utmp.h>
struct utmp *getutent(void);
struct utmp *getutid(struct utmp *ut);
struct utmp *getutline(struct utmp *ut);
struct utmp *pututline(struct utmp *ut);
void setutent(void);
void endutent(void);
void utmpname(const char *file);
utmpname() sets the name of the utmp-format file for the other utmp
functions to access. If
utmpname() is not used to set the filename
before the other functions are used, they assume
_PATH_UTMP, as defined
in
<paths.h>.
setutent() rewinds the file pointer to the beginning of the utmp file. It
is generally a Good Idea to call it before any of the other functions.
endutent() closes the utmp file. It should be called when the user code
is done accessing the file with the other functions.
getutent() reads a line from the current file position in the utmp file.
It returns a pointer to a structure containing the fields of the line.
getutid() searches forward from the current file position in the utmp
file based upon
ut. If
ut->ut_type is one of
RUN_LVL,
BOOT_TIME,
NEW_TIME, or
OLD_TIME,
getutid() will
find the first entry whose
ut_type field matches
ut->ut_type.
If
ut->ut_type is one of
INIT_PROCESS,
LOGIN_PROCESS,
USER_PROCESS, or
DEAD_PROCESS,
getutid() will find the
first entry whose ut_id field matches
ut->ut_id.
getutline() searches forward from the current file position in the utmp
file. It scans entries whose ut_type is
USER_PROCESS or
LOGIN_PROCESS and returns the first one whose ut_line field matches
ut->ut_line.
pututline() writes the utmp structure
ut into the utmp file. It
uses
getutid() to search for the proper place in the file to insert the
new entry. If it cannot find an appropriate slot for
ut,
pututline() will append the new entry to the end of the file.
getutent(),
getutid(),
getutline() and
pututline()
return a pointer to a
struct utmp on success, and NULL on failure. This
struct utmp is allocated in static storage, and may be overwritten by
subsequent calls.
These above functions are not thread-safe. Glibc adds reentrant versions
#define _GNU_SOURCE /* or _SVID_SOURCE or _BSD_SOURCE */
#include <utmp.h>
int getutent_r(struct utmp *ubuf, struct utmp **ubufp);
int getutid_r(struct utmp *ut,
struct utmp *ubuf, struct utmp **ubufp);
int getutline_r(struct utmp *ut,
struct utmp *ubuf, struct utmp **ubufp);
These functions are GNU extensions, analogs of the functions of the same name
without the _r suffix. The
ubuf parameter gives these functions a place
to store their result. On success they return 0, and a pointer to the result
is written in *
ubufp. On error these functions return -1.
The following example adds and removes a utmp record, assuming it is run from
within a pseudo terminal. For usage in a real application, you should check
the return values of getpwuid() and ttyname().
#include <string.h>
#include <stdlib.h>
#include <pwd.h>
#include <unistd.h>
#include <utmp.h>
int main(int argc, char *argv[])
{
struct utmp entry;
system("echo before adding entry:;who");
entry.ut_type=USER_PROCESS;
entry.ut_pid=getpid();
strcpy(entry.ut_line,ttyname(0)+strlen("/dev/"));
/* only correct for ptys named /dev/tty[pqr][0-9a-z] */
strcpy(entry.ut_id,ttyname(0)+strlen("/dev/tty"));
time(&entry.ut_time);
strcpy(entry.ut_user,getpwuid(getuid())->pw_name);
memset(entry.ut_host,0,UT_HOSTSIZE);
entry.ut_addr=0;
setutent();
pututline(&entry);
system("echo after adding entry:;who");
entry.ut_type=DEAD_PROCESS;
memset(entry.ut_line,0,UT_LINESIZE);
entry.ut_time=0;
memset(entry.ut_user,0,UT_NAMESIZE);
setutent();
pututline(&entry);
system("echo after removing entry:;who");
endutent();
return 0;
}
/var/run/utmp database of currently logged-in users
/var/log/wtmp database of past user logins
XPG 2, SVID 2, Linux FSSTND 1.2
In XPG2 and SVID2 the function
pututline() is documented to return void,
and that is what it does on many systems (AIX, HPUX, Linux libc5). HPUX
introduces a new function
_pututline() with the prototype given above
for
pututline() (also found in Linux libc5).
All these functions are obsolete now on non-Linux systems. POSIX 1003.1-2001,
following XPG4.2, does not have any of these functions, but instead uses
#include <utmpx.h>
struct utmpx *getutxent(void);
struct utmpx *getutxid(const struct utmpx *);
struct utmpx *getutxline(const struct utmpx *);
struct utmpx *pututxline(const struct utmpx *);
void setutxent(void);
void endutxent(void);
The
utmpx structure is a superset of the
utmp structure, with
additional fields, and larger versions of the existing fields. The
corresponding files are often
/var/*/utmpx and
/var/*/wtmpx.
Linux glibc on the other hand does not use
utmpx since its
utmp
structure is already large enough. The functions
getutxent etc. are
aliases for
getutent etc.
utmp(5)
