ttyslot
Section: C Library Functions (3)
Updated: 202-0-08
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NAME
ttyslot - find the slot of the current user's terminal in some file
LIBRARY
Standard C library
(
libc,~
-lc)
SYNOPSIS
#include <unistd.h> /* See NOTES */
int ttyslot(void);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
ttyslot():
Since glibc 2.24:
_DEFAULT_SOURCE
From glibc 2.20 to glibc 2.23:
_DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
glibc 2.19 and earlier:
_BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
DESCRIPTION
The legacy function
ttyslot()
returns the index of the current user's entry in some file.
Now "What file?" you ask.
Well, let's first look at some history.
Ancient history
There used to be a file
/etc/ttys
in UNIX V6, that was read by the
init(1)
program to find out what to do with each terminal line.
Each line consisted of three characters.
The first character was either [aq]0[aq] or [aq]1[aq],
where [aq]0[aq] meant "ignore".
The second character denoted the terminal: [aq]8[aq] stood for "/dev/tty8".
The third character was an argument to
getty(8)
indicating the sequence of line speeds to try ([aq]-[aq] was: start trying
110 baud).
Thus a typical line was "18-".
A hang on some line was solved by changing the [aq]1[aq] to a [aq]0[aq],
signaling init, changing back again, and signaling init again.
In UNIX V7 the format was changed: here the second character
was the argument to
getty(8)
indicating the sequence of line speeds to try ([aq]0[aq] was: cycle through
30-120-15-110 baud; [aq]4[aq] was for the o-line console DECwriter)
while the rest of the line contained the name of the tty.
Thus a typical line was "14console".
Later systems have more elaborate syntax.
System -like systems have
/etc/inittab
instead.
Ancient history (2)
On the other hand, there is the file
/etc/utmp
listing the people currently logged in.
It is maintained by
login(1).
It has a fixed size, and the appropriate index in the file was
determined by
login(1)
using the
ttyslot()
call to find the number of the line in
/etc/ttys
(counting from 1).
The semantics of ttyslot
Thus, the function
ttyslot()
returns the index of the controlling terminal of the calling process
in the file
/etc/ttys,
and that is (usually) the same as the index of the entry for the
current user in the file
/etc/utmp.
BSD still has the
/etc/ttys
file, but System -like systems do not, and hence cannot refer to it.
Thus, on such systems the documentation says that
ttyslot()
returns the current user's index in the user accounting data base.
RETURN VALUE
If successful, this function returns the slot number.
On error (e.g., if none of the file descriptors 0, 1, or 2 is
associated with a terminal that occurs in this data base)
it returns 0 on UNIX V6 and V7 and BS-like systems,
but -1 on System -like systems.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
ttyslot()
| Thread safety | M-Unsafe
|
VERSIONS
The utmp file is found in various places on various systems, such as
/etc/utmp,
/var/adm/utmp,
/var/run/utmp.
STANDARDS
None.
HISTORY
SUSv1; marked as LEGACY in SUSv2; removed in POSIX.-2001.
SUSv2 requires -1 on error.
The glibc2 implementation of this function reads the file
_PATH_TTYS,
defined in
<ttyent.h>
as "/etc/ttys".
It returns 0 on error.
Since Linux systems do not usually have "/etc/ttys", it will
always return 0.
On BS-like systems and Linux, the declaration of
ttyslot()
is provided by
<unistd.h>.
On System -like systems, the declaration is provided by
<stdlib.h>.
Since glibc 2.24,
<stdlib.h>
also provides the declaration with the following
feature test macro definitions:
(_XOPEN_SOURCE >= 500 ||
(_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED))
&& ! (_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600)
Minix also has
fttyslot(
fd).
SEE ALSO
getttyent(3),
ttyname(3),
utmp(5)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- Ancient history
-
- Ancient history (2)
-
- The semantics of ttyslot
-
- RETURN VALUE
-
- ATTRIBUTES
-
- VERSIONS
-
- STANDARDS
-
- HISTORY
-
- SEE ALSO
-
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