exec(3) - Linux manual page (original) (raw)

exec(3) Library Functions Manual exec(3)

NAME top

   execl, execlp, execle, execv, execvp, execvpe - execute a file

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <unistd.h>**

   **extern char environ;**

   **int execl(const char ***_pathname_**, const char ***_arg_**, ...**
                   **/*, (char *) NULL */);**
   **int execlp(const char ***_file_**, const char ***_arg_**, ...**
                   **/*, (char *) NULL */);**
   **int execle(const char ***_pathname_**, const char ***_arg_**, ...**
                   **/*, (char *) NULL, char *const** _envp_**[] */);**
   **int execv(const char ***_pathname_**, char *const** _argv_**[]);**
   **int execvp(const char ***_file_**, char *const** _argv_**[]);**
   **int execvpe(const char ***_file_**, char *const** _argv_**[], char *const** _envp_**[]);**

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

   **execvpe**():
       _GNU_SOURCE

DESCRIPTION top

   The **exec**() family of functions replaces the current process image
   with a new process image.  The functions described in this manual
   page are layered on top of [execve(2)](../man2/execve.2.html).  (See the manual page for
   [execve(2)](../man2/execve.2.html) for further details about the replacement of the current
   process image.)

   The initial argument for these functions is the name of a file
   that is to be executed.

   The functions can be grouped based on the letters following the
   "exec" prefix.

l - execl(), execlp(), execle() The const char *arg and subsequent ellipses can be thought of as arg0, arg1, ..., argn. Together they describe a list of one or more pointers to null-terminated strings that represent the argument list available to the executed program. The first argument, by convention, should point to the filename associated with the file being executed. The list of arguments must be terminated by a null pointer, and, since these are variadic functions, this pointer must be cast (char *) NULL.

   By contrast with the 'l' functions, the 'v' functions (below)
   specify the command-line arguments of the executed program as a
   vector.

v - execv(), execvp(), execvpe() The char *const argv[] argument is an array of pointers to null- terminated strings that represent the argument list available to the new program. The first argument, by convention, should point to the filename associated with the file being executed. The array of pointers must be terminated by a null pointer.

e - execle(), execvpe() The environment of the new process image is specified via the argument envp. The envp argument is an array of pointers to null- terminated strings and must be terminated by a null pointer.

   All other **exec**() functions (which do not include 'e' in the
   suffix) take the environment for the new process image from the
   external variable _environ_ in the calling process.

p - execlp(), execvp(), execvpe() These functions duplicate the actions of the shell in searching for an executable file if the specified filename does not contain a slash (/) character. The file is sought in the colon-separated list of directory pathnames specified in the PATH environment variable. If this variable isn't defined, the path list defaults to a list that includes the directories returned by confstr(CSPATH) (which typically returns the value "/bin:/usr/bin") and possibly also the current working directory; see VERSIONS for further details.

   **execvpe**() searches for the program using the value of **PATH** from
   the caller's environment, not from the _envp_ argument.

   If the specified filename includes a slash character, then **PATH** is
   ignored, and the file at the specified pathname is executed.

   In addition, certain errors are treated specially.

   If permission is denied for a file (the attempted [execve(2)](../man2/execve.2.html) failed
   with the error **EACCES**), these functions will continue searching
   the rest of the search path.  If no other file is found, however,
   they will return with _[errno](../man3/errno.3.html)_ set to **EACCES**.

   If the header of a file isn't recognized (the attempted [execve(2)](../man2/execve.2.html)
   failed with the error **ENOEXEC**), these functions will execute the
   shell (_/bin/sh_) with the path of the file as its first argument.
   (If this attempt fails, no further searching is done.)

   All other **exec**() functions (which do not include 'p' in the
   suffix) take as their first argument a (relative or absolute)
   pathname that identifies the program to be executed.

RETURN VALUE top

   The **exec**() functions return only if an error has occurred.  The
   return value is -1, and _[errno](../man3/errno.3.html)_ is set to indicate the error.

ERRORS top

   All of these functions may fail and set _[errno](../man3/errno.3.html)_ for any of the
   errors specified for [execve(2)](../man2/execve.2.html).

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────┬───────────────┬─────────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────┼───────────────┼─────────────┤
   │ **execl**(), **execle**(), **execv**()       │ Thread safety │ MT-Safe     │
   ├──────────────────────────────────┼───────────────┼─────────────┤
   │ **execlp**(), **execvp**(), **execvpe**()    │ Thread safety │ MT-Safe env │
   └──────────────────────────────────┴───────────────┴─────────────┘

VERSIONS top

   The default search path (used when the environment does not
   contain the variable **PATH**) shows some variation across systems.
   It generally includes _/bin_ and _/usr/bin_ (in that order) and may
   also include the current working directory.  On some other
   systems, the current working is included after _/bin_ and _/usr/bin_,
   as an anti-Trojan-horse measure.  The glibc implementation long
   followed the traditional default where the current working
   directory is included at the start of the search path.  However,
   some code refactoring during the development of glibc 2.24 caused
   the current working directory to be dropped altogether from the
   default search path.  This accidental behavior change is
   considered mildly beneficial, and won't be reverted.

   The behavior of **execlp**() and **execvp**() when errors occur while
   attempting to execute the file is historic practice, but has not
   traditionally been documented and is not specified by the POSIX
   standard.  BSD (and possibly other systems) do an automatic sleep
   and retry if **ETXTBSY** is encountered.  Linux treats it as a hard
   error and returns immediately.

   Traditionally, the functions **execlp**() and **execvp**() ignored all
   errors except for the ones described above and **ENOMEM** and **E2BIG**,
   upon which they returned.  They now return if any error other than
   the ones described above occurs.

STANDARDS top

   **environ**
   **execl**()
   **execlp**()
   **execle**()
   **execv**()
   **execvp**()
          POSIX.1-2008.

   **execvpe**()
          GNU.

HISTORY top

   **environ**
   **execl**()
   **execlp**()
   **execle**()
   **execv**()
   **execvp**()
          POSIX.1-2001.

   **execvpe**()
          glibc 2.11.

BUGS top

   Before glibc 2.24, **execl**() and **execle**() employed [realloc(3)](../man3/realloc.3.html)
   internally and were consequently not async-signal-safe, in
   violation of the requirements of POSIX.1.  This was fixed in glibc
   2.24.

Architecture-specific details On sparc and sparc64, execv() is provided as a system call by the kernel (with the prototype shown above) for compatibility with SunOS. This function is not employed by the execv() wrapper function on those architectures.

SEE ALSO top

   **sh**(1), [execve(2)](../man2/execve.2.html), [execveat(2)](../man2/execveat.2.html), [fork(2)](../man2/fork.2.html), [ptrace(2)](../man2/ptrace.2.html), [fexecve(3)](../man3/fexecve.3.html),
   [system(3)](../man3/system.3.html), [environ(7)](../man7/environ.7.html)

COLOPHON top

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Linux man-pages 6.10 2024-07-23 exec(3)

Pages that refer to this page:pmlogger(1), watch(1), xargs(1), execve(2), getpid(2), ptrace(2), seccomp(2), statfs(2), vfork(2), atexit(3), clearenv(3), confstr(3), glob(3), libexpect(3), lttng-ust(3), on_exit(3), pam_getenvlist(3), posix_spawn(3), statvfs(3), stdin(3), sysconf(3), system(3), systemd.exec(5), environ(7), signal-safety(7)