I have the rest of posix_spawn* to send along, but thought I'd get feedback on this page before sending the rest. - bog .\" Copyright (c) 2009 Bill O. Gallmeister (bgallmeister@xxxxxxxxx) .\" .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one. .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" .\" References consulted: .\" Linux glibc source code .\" POSIX 1003.1-2004 documentation (http://www.opengroup.org/onlinepubs/009695399) .\" .TH "POSIX_SPAWN" 3 2009-09-22 "GNU" "Linux Programmer's Manual" .\" posix_spawn .SH NAME posix_spawn, posix_spawnp \- spawn a process .SH SYNOPSIS .nf .B #include <spawn.h> .BI "int posix_spawn(pid_t *" pid ", const char *" path , .BI " const posix_spawn_file_actions_t *" file_actions , .BI " const posix_spawnattr_t *" attrp , .BI " char *const " argv[] ", char *const " envp[] ); .BI "int posix_spawnp(pid_t *" pid ", const char *" file , .BI " const posix_spawn_file_actions_t *" file_actions , .BI " const posix_spawnattr_t *" attrp , .BI " char *const " argv[] ", char *const " envp[] ); .fi .sp .in -4n Feature Test Macro Requirements for glibc (see .BR feature_test_macros (7)): .in .sp .ad l .BR posix_spawn () and .BR posix_spawnp (): (_POSIX_C_SOURCE\ >=\ 200112L)\ &&\ (_POSIX_SPAWN) .ad b .SH DESCRIPTION .BR Posix_spawn () and .BR posix_spawnp () are used to create a new child process from the specified process image. Think of these functions as a combined .BR fork ()/ exec (). This page documents the behavior of the GNU/Linux implementations of these functions. .LP .BR Posix_spawn () and .BR posix_spawnp () are not meant to replace .BR fork () and .BR exec (). In fact, these functions provide only a subset of the functionality that can be achieved by using the more common system calls. These functions were specified by POSIX provide the standardized capability to create new processes on machines that lack the capability to support the .BR fork () system call. These machines are generally small, embedded systems lacking MMU support. .SH DESCRIPTION .BR Posix_spawn () and .BR posix_spawnp () provide the functionality of a combined .BR fork () and .BR exec (), with some optional housekeeping steps in the child process before the .BR exec (). These functions will be described in terms of a three step process: the fork step, the pre-exec step, and the exec step. .SS FORK step Each function executes a .BR fork (), or possibly a .BR vfork () (more on .BR vfork () below). In the parent, the .I pid argument is dereferenced and the pid of the child is stored there. The parent then returns from the .BR spawn () function. .BR Wait (), .BR wait3 (), or .BR waitpid () can be used to check the status of the child process after this point. If the child fails in any of its housekeeping or fails to execute the desired file, the child will exit with the exit value of 127. .IP "WHEN IS VFORK USED?" 2 .BR vfork () is used instead of .BR fork () when: .IP * the .I spawn-flags element of *attrp contains the value POSIX_SPAWN_USEVFORK and does \fInot\fP contain POSIX_SPAWN_SETSIGMASK, POSIX_SPAWN_SETSIGDEF, POSIX_SPAWN_SETSCHEDPARAM, POSIX_SPAWN_SETSCHEDULER, POSIX_SPAWN_SETPGROUP, or POSIX_SPAWN_RESETIDS. .IP * .I file_actions is NULL. .LP In essence, .BR vfork () is used only if the caller requests it, and if there is no cleanup expected in the child before it .BR execs the requested file. .SS PRE-EXEC STEP: GENERAL PROCESSING In between the .BR fork () and the .BR exec (), a child process has a certain set of hosekeeping operations it may need to perform. .BR Posix_spawn () and .BR posix_spawnp () support a small, well-defined set of system tasks that the child process can accomplish before it executes the executable file. These operations are controlled by the attributes structure pointed to by attrp, as well as the vector .I file_actions. In the child, processing is done in the following sequence: .IP 1. 5 General processing: signal mask, signal default handlers, scheduling algorithm and parameters, process group, UID and GID are changed as specified by the .I attrp argument. .IP 2. 5 File actions, as specified in the .I file_actions argument, are performed in order, starting with .I file_actions[0] and continuing to the end of the list. .IP 3. 5 Files with the FD_CLOEXEC flag are closed. .LP The general processing operations are: .IP * 2 set signal mask and default actions. .IP * set effective group and user ID .IP * set process group .IP * set scheduling algorithm and/or scheduling parameters (if POSIX_PROCESS_SCHEDULING is in effect) .IP * a sequence of .BR open (), .BR close (), and .BR dup2 () actions .LP In addition, standard operations that occur on .BR fork () and .BR exec (), can also be expected to occur, including: closing of files based on the FD_CLOEXEC flag. effect on threads in the forked process (including .BR pthread_atfork ()). .LP The housekeeping activities in the child are controlled by the object pointed to by .I attrp (for non-file actions), and by the array of .I file_actions (described in the section following this one). In POSIX parlance, these objects are not referred to as structures, and their elements are not specified by name. For portable coding, you should initialize and set values in these structures only using the POSIX-specified functions. .LP Based on the .I spawn-flags specified in the structure pointed to by .I attrp, the child process can: .IP [POSIX_SPAWN_SETSIGMASK] 2 Set its signal mask as if using .BI sigprocmask( SIG_SETMASK ) and the signal set specified in the .I spawn-sigmask element. .IP [POSIX_SPAWN_SETSIGDEF] Reset the handler for all signals specified in the .I spawn-sigdefault element back to default state. .IP [POSIX_SPAWN_SETSCHEDPARAM] Set the scheduling parameters (POSIX_PRIORITY_SCHEDULING only) to the parameters specified in the .I spawn-schedparam element. .IP [POSIX_SPAWN_SETSCHEDULER] Set the scheduling algorithm and parameters according to the .I spawn-schedpolicy element of .I *attrp (If .I POSIX_SPAWN_SETSCHEDPARAM is also set, then the scheduling parameters are set according to the corresponding element; otherwise, the effect is as if a NULL was passed as the .I param argument to .BR sched_setscheduler ()). .IP [POSIX_SPAWN_RESETIDS] Set the effective UID and GID to the real UID and GID of the parent process. If this flag is not set, then the child gets the effective UID and GID of the parent. In either case, the setuid and setgid bits of the executable file themselves take precedence. .IP [POSIX_SPAWN_SETPGROUP] Set the process group to the value specified in the .I spawn-pgroup element .LP If any of these actions fails (due to bogus values being passed or other reasons why signal handling, process scheduling, and process ID functions might fail), the child process exits with exit value 127. .LP To set these flags, use .BR posix_spawnattr_init () and .BR posix_spawnattr_setflags (). Additionally, you should call .BR posix_spawnattr_destroy () when you are done with the structure pointed to by .I attrp. The POSIX standard tells you to call this function to de-initialize the structure pointed to by attrp when you are done with it; however, on Linux systems this operation is a no-op. .LP To set the various elements in the .I posix_spawnattr_t object, use: .IP \fIspawn-sigmask\fP 2 .BR posix_spawnattr_setsigmask () .IP \fIspawn-sigdefault\fP .BR posix_spawnattr_setsigdefault () .IP \fIspawn-schedpolicy\fP .BR posix_spawnattr_setschedpolicy () .IP \fIspawn-schedparam\fP .BR posix_spawnattr_setschedparam () .IP \fIspawn-pgroup\fP .BR posix_spawnattr_setproup () .LP There are "get" variants of all of the above functions as well. .SS PRE-EXEC STEP: FILE PROCESSING The argument .I file_actions specifies a sequence of file operations which are performed in the child process after the general processing described above, and before it .I execs . If .I file_actions is NULL, then no special action is taken, and standard .BR exec () sematics apply--files open before the exec remain open in the new process, except those for which the FD_CLOEXEC flag has been set. File locks remain in place. .LP If .I file_actions is not NULL, then it contains an ordered set of requests to .BR open (), .BR close (), and .BR dup2 () files. These requests are added to the .I file_actions by .BR posix_spawn_file_actions_addopen (), .BR posix_spawn_file_actions_addclose (), and .BR posix_spawn_file_actions_adddup2 (). The requested operations are performed in the order they were added to .I file_actions . Note that you can specify file descriptors in .I posix_spawn_file_actions_adddup2 () which would not be usable if you called .BR dup2 () at that time--I.E. file descriptors that are opened or closed by the earlier operations added to .I file_actions . .SS EXEC Step Once the child has successfully forked and performed all requested pre-exec steps, the child runs the requested executable. .LP .BR Posix_spawn () requires the user to specify the full path of the file to be executed, similar to .BR execl (). .BR Posix_spawnp () allows the user to specify an executable file name, and uses the PATH environment variable to look up the executable program, like .BR execlp (). Other than that, the two functions are identical. .LP The child process takes its environment from the .I envp argument, which is interpreted as if it had been passed to .BR execle (). The arguments to the created process come from the .I argv argument, which is processed as for any of the .BR exec () family. .SH RETURN VALUE .LP Upon successful completion, .BR posix_spawn () and .BR posix_spawnp () set the PID of the child process in .I pid, and return 0. If there is an error before (or in the process of) the .BR fork (), then no child is created, and these functions return an error value as described below. .LP If the parent is able to successfully .BR fork () the child, but the child fails to perform any of the requested actions prior to .BR exec (), or if the .BR exec () itself fails, then the child will exit with status 127. .SH ERRORS .LP .BR posix_spawn () and .BR posix_spawnp () fail only in the case where the underlying .BR fork () or .BR vfork () call fail; in these cases, the error return will be the errno value set by .BR fork () or .BR vfork (). .LP If the child process is successfully forked, then .BR posix_spawn () and .BR posix_spawnp () both return success. However, the child process may still fail for a plethora of reasons related to its pre-\fBexec\fR() initialization. In all of these cases, the child process will exit with the exit value of 127. .LP In addition, these functions fail if: .TP .B ENOSYS Function not supported on this system. .SH NOTES POSIX does not specify the names of any internal elements within the .I posix_spawnattr_t structure; in fact, it does not specify that it is a structure at all. Portable programs should refrain from directly referencing fields within this structure. In these man pages we refer to the internal parts of the .I posix_spawnattr_t as elements. .SH CONFORMING TO .LP POSIX.1-2004. .SH SEE ALSO .LP .BR close (2), .BR dup2 (2), .BR execl (2), .BR execlp (2), .BR fork (2), .BR open (2), .BR sched_setparam (2), .BR sched_setscheduler (2), .BR setpgid (2), .BR setuid (2), .BR sigaction (2), .BR sigprocask (2), .BR posix_spawnattr_destroy (3), .BR posix_spawnattr_getflags (3), .BR posix_spawnattr_getpgroup (3), .BR posix_spawnattr_getschedparam (3), .BR posix_spawnattr_getschedpolicy (3), .BR posix_spawnattr_getsigdefault (3), .BR posix_spawnattr_getsigmask (3), .BR posix_spawnattr_init (3), .BR posix_spawnattr_setflags (3), .BR posix_spawnattr_setpgroup (3), .BR posix_spawnattr_setschedparam (3), .BR posix_spawnattr_setschedpolicy (3), .BR posix_spawnattr_setsigdefault (3), .BR posix_spawnattr_setsigmask (3), .BR posix_spawn_file_actions_addclose (3), .BR posix_spawn_file_actions_adddup2 (3), .BR posix_spawn_file_actions_addopen (3), .BR posix_spawn_file_actions_destroy (3), .BR posix_spawn_file_actions_init (3), .BR pthread_atfork (3), .BR <spawn.h>, Base Definitions volume of POSIX.1-2004, .I http://www.opengroup.org/unix/online.html -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
