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.\" ======================================================================== |
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.\" |
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.IX Title "libptytty 3" |
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.TH libptytty 3 "2016-02-25" "1.8" "LIBPTYTTY" |
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.\" For nroff, turn off justification. Always turn off hyphenation; it makes |
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.\" way too many mistakes in technical documents. |
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.if n .ad l |
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.nh |
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.SH "NAME" |
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libptytty \- OS independent and secure pty/tty and utmp/wtmp/lastlog handling |
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.SH "SYNOPSIS" |
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.IX Header "SYNOPSIS" |
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.Vb 1 |
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\& cc ... \-lptytty |
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\& |
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\& #include <libptytty.h> |
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\& |
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\& |
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\& // C++ |
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\& ptytty *pty = ptytty::create (); |
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\& |
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\& if (!pty\->get ()) |
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\& // error allocating pty |
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\& |
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\& if (we want utmp) |
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\& pty\->login (process_pid, 0, "remote.host"); |
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\& else if (we want utmp AND wtmp/lastlog) |
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\& pty\->login (process_pid, 1, "remote.host"); |
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\& |
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\& // we are done with it |
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\& delete pty; |
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\& |
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\& |
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\& // C |
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\& PTYTTY pty = ptytty_create (); |
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\& |
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\& if (!ptytty_get (pty)) |
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\& // error allocating pty |
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\& |
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\& if (we want utmp) |
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\& ptytty_login (pty, process_pid, 0, "remote.host"); |
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\& else if (we want utmp AND wtmp/lastlog) |
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\& ptytty_login (pty, process_pid, 1, "remote.host"); |
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\& |
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\& // we are done with it |
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\& ptytty_delete (pty); |
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.Ve |
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.PP |
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See also the \fIeg/\fR directory, which currently contains the \fIc\-sample.c\fR |
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file that spawns a login shell from C using libptytty. |
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.SH "DESCRIPTION" |
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.IX Header "DESCRIPTION" |
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Libptytty is a small library that offers pseudo-tty management in an |
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OS-independent way. It was created out of frustration over the many |
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differences of pty/tty handling in different operating systems for the use |
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inside \f(CW\*(C`rxvt\-unicode\*(C'\fR. |
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.PP |
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In addition to offering mere pty/tty management, it also offers session |
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database support (utmp and optional wtmp/lastlog updates for login |
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shells). |
193 |
.PP |
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It also supports fork'ing after startup and dropping privileges in the |
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calling process, so in case the calling process gets compromised by the |
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user starting the program there is less to gain, as only the helper |
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process runs with privileges (e.g. setuid/setgid), which reduces the area |
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of attack immensely. |
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.PP |
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Libptytty is written in \*(C+, but it also offers a C\-only \s-1API.\s0 |
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.SH "SECURITY CONSIDERATIONS" |
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.IX Header "SECURITY CONSIDERATIONS" |
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\&\fI\f(BIIt is of paramount importance that you at least read the following |
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paragraph!\fI\fR |
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.PP |
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If you write a typical terminal-like program that just wants one or more |
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ptys, you should call the \f(CW\*(C`ptytty::init ()\*(C'\fR method (C: \f(CW\*(C`ptytty_init ()\*(C'\fR |
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function) as the very first thing in your program: |
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.PP |
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.Vb 5 |
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\& int main (int argc, char *argv[]) |
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\& { |
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\& // do nothing here |
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\& ptytty::init (); |
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\& // in C: ptytty_init (); |
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\& |
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\& // initialise, parse arguments, etc. |
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\& } |
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.Ve |
220 |
.PP |
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This checks whether the program runs setuid or setgid. If yes then it will |
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fork a helper process and drop privileges. |
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.PP |
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Some programs need finer control over if and when this helper process |
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is started, and if and how to drop privileges. For those programs, the |
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methods \f(CW\*(C`ptytty::use_helper\*(C'\fR and \f(CW\*(C`ptytty::drop_privileges\*(C'\fR (and possibly |
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\&\f(CW\*(C`ptytty::sanitise_stdfd\*(C'\fR) are more useful. |
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.SH "\*(C+ INTERFACE: THE ptytty CLASS" |
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.IX Header " INTERFACE: THE ptytty CLASS" |
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.SS "\s-1STATIC METHODS\s0" |
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.IX Subsection "STATIC METHODS" |
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.IP "ptytty::init ()" 4 |
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.IX Item "ptytty::init ()" |
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The default way to initialise libptytty. Must be called immediately as |
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the first thing in the \f(CW\*(C`main\*(C'\fR function, or earlier e.g. during static |
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construction time. The earlier, the better. |
237 |
.Sp |
238 |
This method calls \f(CW\*(C`sanitise_stdfd\*(C'\fR and then checks whether the program runs |
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with setuid/setgid permissions and, if yes, spawns a helper process for |
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pty/tty management. It then drops the privileges completely, so the actual |
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program runs without setuid/setgid privileges. |
242 |
.Sp |
243 |
On failure, this method terminates the process. |
244 |
.IP "ptytty::use_helper ()" 4 |
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.IX Item "ptytty::use_helper ()" |
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Tries to start a helper process that retains privileges even when the |
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calling process does not. This is usually called from \f(CW\*(C`ptytty::init\*(C'\fR when |
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it detects that the program is running setuid or setgid, but can be called |
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manually if it is inconvenient to drop privileges at startup, or when |
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you are not running setuid/setgid but want to drop privileges (e.g. when |
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running as a root-started daemon). |
252 |
.Sp |
253 |
This method will try not to start more than one helper process. The same |
254 |
helper process can usually be used both from the process starting it and |
255 |
all its fork'ed (not exec'ed) children. |
256 |
.Sp |
257 |
On failure, this method terminates the process. |
258 |
.IP "ptytty::drop_privileges ()" 4 |
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.IX Item "ptytty::drop_privileges ()" |
260 |
Drops privileges completely, i.e. sets real, effective and saved user |
261 |
id to the real user id. Useful to make sure that the process doesn't |
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run with special privileges. |
263 |
.Sp |
264 |
On failure, this method terminates the process. |
265 |
.IP "ptytty::sanitise_stdfd ()" 4 |
266 |
.IX Item "ptytty::sanitise_stdfd ()" |
267 |
Checks whether file descriptors 0, 1 and 2 (stdin, stdout and stderr) |
268 |
are valid (open) and, if not, connects them to \fI/dev/tty\fR or |
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\&\fI/dev/null\fR if possible. This is necessary because libptytty might |
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want to output error messages to those descriptors, which at the time |
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of outputting the error message, might be connected to something |
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unsuitable opened by the unsuspecting program itself (this can be a |
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security issue). |
274 |
.Sp |
275 |
On failure, this method terminates the process. |
276 |
.IP "bool success = ptytty::send_fd (int socket, int fd)" 4 |
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.IX Item "bool success = ptytty::send_fd (int socket, int fd)" |
278 |
Utility method to send a file descriptor over a unix domain |
279 |
socket. Returns true if successful, false otherwise. This method is only |
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exposed for your convenience and is not required for normal operation. |
281 |
.IP "int fd = ptytty::recv_fd (int socket)" 4 |
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.IX Item "int fd = ptytty::recv_fd (int socket)" |
283 |
Utility method to receive a file descriptor over a unix domain |
284 |
socket. Returns the fd if successful and \f(CW\*(C`\-1\*(C'\fR otherwise. This method |
285 |
is only exposed for your convenience and is not required for normal |
286 |
operation. |
287 |
.IP "ptytty *pty = ptytty::create ()" 4 |
288 |
.IX Item "ptytty *pty = ptytty::create ()" |
289 |
Creates new ptytty object. Creation does not yet do anything besides |
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allocating the structure. |
291 |
.Sp |
292 |
A static method is used because the actual ptytty implementation can |
293 |
differ at runtime, so you need a dynamic object creation facility. |
294 |
.SS "\s-1DYNAMIC/SESSION\-RELATED DATA MEMBERS AND METHODS\s0" |
295 |
.IX Subsection "DYNAMIC/SESSION-RELATED DATA MEMBERS AND METHODS" |
296 |
.IP "int pty_fd = pty\->pty" 4 |
297 |
.IX Item "int pty_fd = pty->pty" |
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.PD 0 |
299 |
.IP "int tty_fd = pty\->tty" 4 |
300 |
.IX Item "int tty_fd = pty->tty" |
301 |
.PD |
302 |
These members contain the pty and tty file descriptors, respectively. They |
303 |
initially contain \f(CW\*(C`\-1\*(C'\fR until a successful call to \f(CW\*(C`ptytty::get\*(C'\fR. |
304 |
.IP "bool success = pty\->get ()" 4 |
305 |
.IX Item "bool success = pty->get ()" |
306 |
Tries to find, allocate and initialise a new pty/tty pair. Returns \f(CW\*(C`true\*(C'\fR |
307 |
when successful. |
308 |
.Sp |
309 |
If the helper process is running and there is a protocol error, this |
310 |
method terminates the process. |
311 |
.IP "pty\->login (int cmd_pid, bool login_shell, const char *hostname)" 4 |
312 |
.IX Item "pty->login (int cmd_pid, bool login_shell, const char *hostname)" |
313 |
Creates an entry in the systems session database(s) (utmp, wtmp, lastlog). |
314 |
\&\f(CW\*(C`cmd_pid\*(C'\fR must be the pid of the process representing the session |
315 |
(such as the login shell), \f(CW\*(C`login_shell\*(C'\fR defines whether the session is |
316 |
associated with a login, which influences whether wtmp and lastlog entries |
317 |
are created, and \f(CW\*(C`hostname\*(C'\fR should identify the \*(L"hostname\*(R" the user logs |
318 |
in from, which often is the value of the \f(CW\*(C`DISPLAY\*(C'\fR variable or tty line |
319 |
in case of local logins. |
320 |
.Sp |
321 |
Calling this method is optional. A session starts at the time of the login |
322 |
call and extends until the ptytty object is destroyed. |
323 |
.IP "pty\->close_tty ()" 4 |
324 |
.IX Item "pty->close_tty ()" |
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Closes the tty. Useful after forking in the parent/pty process. |
326 |
.IP "bool success = pty\->make_controlling_tty ()" 4 |
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.IX Item "bool success = pty->make_controlling_tty ()" |
328 |
Tries to make the pty/tty pair the controlling terminal of the current |
329 |
process. Useful after forking in the child/tty process. |
330 |
.IP "pty\->set_utf8_mode (bool on)" 4 |
331 |
.IX Item "pty->set_utf8_mode (bool on)" |
332 |
On systems supporting special \s-1UTF\-8\s0 line disciplines (e.g. Linux), this |
333 |
tries to enable this discipline for the given pty. Can be called at any |
334 |
time to change the mode. |
335 |
.SH "C INTERFACE: THE ptytty FAMILY OF FUNCTIONS" |
336 |
.IX Header "C INTERFACE: THE ptytty FAMILY OF FUNCTIONS" |
337 |
.IP "ptytty_init ()" 4 |
338 |
.IX Item "ptytty_init ()" |
339 |
See \f(CW\*(C`ptytty::init ()\*(C'\fR. |
340 |
.IP "\s-1PTYTTY\s0 ptytty_create ()" 4 |
341 |
.IX Item "PTYTTY ptytty_create ()" |
342 |
Creates a new opaque \s-1PTYTTY\s0 object and returns it. Do not try to access it |
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in any way except by testing it for truthness (e.g. \f(CW\*(C`if (pty) ....\*(C'\fR). See |
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\&\f(CW\*(C`ptytty::create ()\*(C'\fR. |
345 |
.IP "int ptytty_pty (\s-1PTYTTY\s0 ptytty)" 4 |
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.IX Item "int ptytty_pty (PTYTTY ptytty)" |
347 |
Return the pty file descriptor. See \f(CW\*(C`pty\->pty\*(C'\fR. |
348 |
.IP "int ptytty_tty (\s-1PTYTTY\s0 ptytty)" 4 |
349 |
.IX Item "int ptytty_tty (PTYTTY ptytty)" |
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Return the tty file descriptor. See \f(CW\*(C`pty\->tty\*(C'\fR. |
351 |
.IP "void ptytty_delete (\s-1PTYTTY\s0 ptytty)" 4 |
352 |
.IX Item "void ptytty_delete (PTYTTY ptytty)" |
353 |
Destroys the \s-1PTYTTY\s0 object, freeing the pty/tty pair and cleaning up the |
354 |
utmp/wtmp/lastlog databases, if initialised/used. Same as \f(CW\*(C`delete pty\*(C'\fR in |
355 |
\&\*(C+. |
356 |
.IP "int ptytty_get (\s-1PTYTTY\s0 ptytty)" 4 |
357 |
.IX Item "int ptytty_get (PTYTTY ptytty)" |
358 |
See \f(CW\*(C`pty\->get\*(C'\fR, returns 0 in case of an error, non-zero otherwise. |
359 |
.IP "void ptytty_login (\s-1PTYTTY\s0 ptytty, int cmd_pid, bool login_shell, const char *hostname)" 4 |
360 |
.IX Item "void ptytty_login (PTYTTY ptytty, int cmd_pid, bool login_shell, const char *hostname)" |
361 |
See \f(CW\*(C`pty\->login\*(C'\fR. |
362 |
.IP "void ptytty_close_tty (\s-1PTYTTY\s0 ptytty)" 4 |
363 |
.IX Item "void ptytty_close_tty (PTYTTY ptytty)" |
364 |
See \f(CW\*(C`pty\->close_tty\*(C'\fR. |
365 |
.IP "int ptytty_make_controlling_tty (\s-1PTYTTY\s0 ptytty)" 4 |
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.IX Item "int ptytty_make_controlling_tty (PTYTTY ptytty)" |
367 |
See \f(CW\*(C`pty\->make_controlling_tty\*(C'\fR. |
368 |
.IP "void ptytty_set_utf8_mode (\s-1PTYTTY\s0 ptytty, int on)" 4 |
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.IX Item "void ptytty_set_utf8_mode (PTYTTY ptytty, int on)" |
370 |
See \f(CW\*(C`pty\->set_utf8_mode\*(C'\fR. |
371 |
.IP "void ptytty_drop_privileges ()" 4 |
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.IX Item "void ptytty_drop_privileges ()" |
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See \f(CW\*(C`ptytty::drop_privileges\*(C'\fR. |
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.IP "void ptytty_use_helper ()" 4 |
375 |
.IX Item "void ptytty_use_helper ()" |
376 |
See \f(CW\*(C`ptytty::use_helper\*(C'\fR. |
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.SH "BUGS" |
378 |
.IX Header "BUGS" |
379 |
You kiddin'? |
380 |
.SH "AUTHORS" |
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.IX Header "AUTHORS" |
382 |
Emanuele Giaquinta <e.giaquinta@glauco.it>, Marc Alexander Lehmann |
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<rxvt\-unicode@schmorp.de>. |