spawn

#include <spawn.h>
int posix_spawn(pid_t *restrict pid, const char *restrict path, const posix_spawn_file_actions_t *restrict file_actions, const posix_spawnattr_t *restrict attrp, char *const argv[restrict], char *const envp[restrict]);

pid_t *restrict pid
    A pointer to a pid_t variable where the process ID of the newly created child process will be stored upon successful return.

const char *restrict path
    The path to the executable file that the new child process will run. This must be an absolute or relative path to a regular executable file.

const posix_spawn_file_actions_t *restrict file_actions
    A pointer to a structure that specifies a series of file descriptor actions (e.g., open, close, dup2) to be performed in the child process before it executes the new program. Can be NULL if no special actions are needed.

const posix_spawnattr_t *restrict attrp
    A pointer to a structure that specifies various attributes for the new process, such as process group, signal mask, scheduling policy, and flags. Can be NULL if default attributes are desired.

char *const argv[restrict]
    An array of pointers to null-terminated strings, representing the argument list for the new process. The last element of this array must be a NULL pointer.

char *const envp[restrict]
    An array of pointers to null-terminated strings, representing the environment for the new process. Each string should be of the form 'KEY=VALUE'. The last element of this array must be a NULL pointer.

The posix_spawn function is a POSIX-standardized interface for creating new processes, designed as a more robust and often more efficient alternative to the traditional combination of fork() and execve(). While not a direct command-line utility, it's a fundamental C library function widely used in Linux and Unix-like operating systems for programmatically launching other executables.

Unlike fork() which duplicates the current process (including its memory space), followed by execve() to replace the child's memory with the new program, posix_spawn combines these steps into a single atomic operation. This can lead to significant performance benefits, especially in scenarios where the parent process has a large memory footprint, as it avoids unnecessary memory copying. It also provides a cleaner way to specify file descriptor actions (like closing or redirecting) and process attributes (like signal masks or scheduling policies) for the new child process before it even starts executing.

Its primary use is within C/C++ applications that need to launch external programs in a controlled and efficient manner, particularly in multi-threaded environments where fork() can introduce complexities due to its interaction with threads and mutexes.

posix_spawn is a C library function, not a command-line utility executable directly from a shell. Its usage is confined to programming in C/C++ or other languages with bindings to libc. While generally more efficient, the exact performance benefits compared to fork/exec can vary depending on the specific operating system and workload. Correct handling of the posix_spawn_file_actions_t and posix_spawnattr_t structures requires careful initialization and understanding of their respective functions (e.g., posix_spawn_file_actions_init(), posix_spawnattr_init()).

Upon successful completion, posix_spawn returns 0. Otherwise, an error number is returned, and no child process is created. Standard error numbers like EACCES, ENOENT, ENOMEM, etc., may be returned.

posix_spawn offers several advantages:
1. Efficiency: Can be significantly faster, especially for large parent processes, as it may avoid copying the entire address space that fork() typically performs.
2. Atomicity: Combines the two operations into one, reducing race conditions.
3. Resource Management: Provides a cleaner interface for configuring file descriptors and process attributes before the new program starts.
4. Multithreaded Safety: Generally safer to use in multi-threaded applications compared to fork() which has limitations on what can be safely called between the fork() and exec().

The posix_spawn function was introduced as part of the POSIX.1-2001 standard. Its primary motivation was to provide a more efficient and robust method for process creation, especially to address the performance overhead associated with fork() (which involves copying the parent's address space) and to offer a safer alternative in multi-threaded programs where fork()'s behavior can be problematic due to its 'async-signal-safe' restrictions before an exec call. It aims to combine the functionality of fork() and execve() into a single, often optimized, system call.

fork(2), exec(3), execve(2), wait(2), posix_spawnattr_init(3), posix_spawn_file_actions_init(3)