diff options
Diffstat (limited to 'man/man3/ttyslot.3')
| -rw-r--r-- | man/man3/ttyslot.3 | 169 |
1 files changed, 169 insertions, 0 deletions
diff --git a/man/man3/ttyslot.3 b/man/man3/ttyslot.3 new file mode 100644 index 000000000..358ae5584 --- /dev/null +++ b/man/man3/ttyslot.3 @@ -0,0 +1,169 @@ +'\" t +.\" Copyright (C) 2002 Andries Brouwer <aeb@cwi.nl> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.\" This replaces an earlier man page written by Walter Harms +.\" <walter.harms@informatik.uni-oldenburg.de>. +.\" +.TH ttyslot 3 (date) "Linux man-pages (unreleased)" +.SH NAME +ttyslot \- find the slot of the current user's terminal in some file +.SH LIBRARY +Standard C library +.RI ( libc ", " \-lc ) +.SH SYNOPSIS +.nf +.BR "#include <unistd.h>" " /* See NOTES */" +.P +.B "int ttyslot(void);" +.fi +.P +.RS -4 +Feature Test Macro Requirements for glibc (see +.BR feature_test_macros (7)): +.RE +.P +.BR ttyslot (): +.nf + 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) +.fi +.SH DESCRIPTION +The legacy function +.BR ttyslot () +returns the index of the current user's entry in some file. +.P +Now "What file?" you ask. +Well, let's first look at some history. +.SS Ancient history +There used to be a file +.I /etc/ttys +in UNIX\ V6, that was read by the +.BR 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 +.BR 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. +.P +In UNIX\ V7 the format was changed: here the second character +was the argument to +.BR getty (8) +indicating the sequence of line speeds to try (\[aq]0\[aq] was: cycle through +300-1200-150-110 baud; \[aq]4\[aq] was for the on-line console DECwriter) +while the rest of the line contained the name of the tty. +Thus a typical line was "14console". +.P +Later systems have more elaborate syntax. +System V-like systems have +.I /etc/inittab +instead. +.SS Ancient history (2) +On the other hand, there is the file +.I /etc/utmp +listing the people currently logged in. +It is maintained by +.BR login (1). +It has a fixed size, and the appropriate index in the file was +determined by +.BR login (1) +using the +.BR ttyslot () +call to find the number of the line in +.I /etc/ttys +(counting from 1). +.SS The semantics of ttyslot +Thus, the function +.BR ttyslot () +returns the index of the controlling terminal of the calling process +in the file +.IR /etc/ttys , +and that is (usually) the same as the index of the entry for the +current user in the file +.IR /etc/utmp . +BSD still has the +.I /etc/ttys +file, but System V-like systems do not, and hence cannot refer to it. +Thus, on such systems the documentation says that +.BR ttyslot () +returns the current user's index in the user accounting data base. +.SH 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 BSD-like systems, +but \-1 on System V-like systems. +.SH ATTRIBUTES +For an explanation of the terms used in this section, see +.BR attributes (7). +.TS +allbox; +lbx lb lb +l l l. +Interface Attribute Value +T{ +.na +.nh +.BR ttyslot () +T} Thread safety MT-Unsafe +.TE +.SH VERSIONS +The utmp file is found in various places on various systems, such as +.IR /etc/utmp , +.IR /var/adm/utmp , +.IR /var/run/utmp . +.SH STANDARDS +None. +.SH HISTORY +SUSv1; marked as LEGACY in SUSv2; removed in POSIX.1-2001. +SUSv2 requires \-1 on error. +.P +The glibc2 implementation of this function reads the file +.BR _PATH_TTYS , +defined in +.I <ttyent.h> +as "/etc/ttys". +It returns 0 on error. +Since Linux systems do not usually have "/etc/ttys", it will +always return 0. +.P +On BSD-like systems and Linux, the declaration of +.BR ttyslot () +is provided by +.IR <unistd.h> . +On System V-like systems, the declaration is provided by +.IR <stdlib.h> . +Since glibc 2.24, +.I <stdlib.h> +also provides the declaration with the following +feature test macro definitions: +.P +.in +4n +.EX +(_XOPEN_SOURCE >= 500 || + (_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED)) + && ! (_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600) +.EE +.in +.P +Minix also has +.IR fttyslot ( fd ). +.\" .SH HISTORY +.\" .BR ttyslot () +.\" appeared in UNIX V7. +.SH SEE ALSO +.BR getttyent (3), +.BR ttyname (3), +.BR utmp (5) |