execveat(2) - Linux manual page (original) (raw)


execveat(2) System Calls Manual execveat(2)

NAME top

   execveat - execute program relative to a directory file descriptor

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <linux/fcntl.h>** /* Definition of **AT_*** constants */
   **#include <unistd.h>**

   **int execveat(int** _dirfd_**, const char ***_pathname_**,**
                **char *const _Nullable** _argv_**[],**
                **char *const _Nullable** _envp_**[],**
                **int** _flags_**);**

DESCRIPTION top

   The **execveat**() system call executes the program referred to by the
   combination of _dirfd_ and _pathname_.  It operates in exactly the
   same way as [execve(2)](../man2/execve.2.html), except for the differences described in
   this manual page.

   If the pathname given in _pathname_ is relative, then it is
   interpreted relative to the directory referred to by the file
   descriptor _dirfd_ (rather than relative to the current working
   directory of the calling process, as is done by [execve(2)](../man2/execve.2.html) for a
   relative pathname).

   If _pathname_ is relative and _dirfd_ is the special value **AT_FDCWD**,
   then _pathname_ is interpreted relative to the current working
   directory of the calling process (like [execve(2)](../man2/execve.2.html)).

   If _pathname_ is absolute, then _dirfd_ is ignored.

   If _pathname_ is an empty string and the **AT_EMPTY_PATH** flag is
   specified, then the file descriptor _dirfd_ specifies the file to be
   executed (i.e., _dirfd_ refers to an executable file, rather than a
   directory).

   The _flags_ argument is a bit mask that can include zero or more of
   the following flags:

   **AT_EMPTY_PATH**
          If _pathname_ is an empty string, operate on the file
          referred to by _dirfd_ (which may have been obtained using
          the [open(2)](../man2/open.2.html) **O_PATH** flag).

   **AT_SYMLINK_NOFOLLOW**
          If the file identified by _dirfd_ and a non-NULL _pathname_ is
          a symbolic link, then the call fails with the error **ELOOP**.

RETURN VALUE top

   On success, **execveat**() does not return.  On error, -1 is returned,
   and _[errno](../man3/errno.3.html)_ is set to indicate the error.

ERRORS top

   The same errors that occur for [execve(2)](../man2/execve.2.html) can also occur for
   **execveat**().  The following additional errors can occur for
   **execveat**():

   _pathname_
          is relative but _dirfd_ is neither **AT_FDCWD** nor a valid file
          descriptor.

   **EINVAL** Invalid flag specified in _flags_.

   **ELOOP** _flags_ includes **AT_SYMLINK_NOFOLLOW** and the file identified
          by _dirfd_ and a non-NULL _pathname_ is a symbolic link.

   **ENOENT** The program identified by _dirfd_ and _pathname_ requires the
          use of an interpreter program (such as a script starting
          with "#!"), but the file descriptor _dirfd_ was opened with
          the **O_CLOEXEC** flag, with the result that the program file
          is inaccessible to the launched interpreter.  See BUGS.

   **ENOTDIR**
          _pathname_ is relative and _dirfd_ is a file descriptor
          referring to a file other than a directory.

STANDARDS top

   Linux.

HISTORY top

   Linux 3.19, glibc 2.34.

NOTES top

   In addition to the reasons explained in [openat(2)](../man2/openat.2.html), the **execveat**()
   system call is also needed to allow [fexecve(3)](../man3/fexecve.3.html) to be implemented
   on systems that do not have the _/proc_ filesystem mounted.

   When asked to execute a script file, the _argv[0]_ that is passed to
   the script interpreter is a string of the form _/dev/fd/N_ or
   _/dev/fd/N/P_, where _N_ is the number of the file descriptor passed
   via the _dirfd_ argument.  A string of the first form occurs when
   **AT_EMPTY_PATH** is employed.  A string of the second form occurs
   when the script is specified via both _dirfd_ and _pathname_; in this
   case, _P_ is the value given in _pathname_.

   For the same reasons described in [fexecve(3)](../man3/fexecve.3.html), the natural idiom
   when using **execveat**() is to set the close-on-exec flag on _dirfd_.
   (But see BUGS.)

BUGS top

   The **ENOENT** error described above means that it is not possible to
   set the close-on-exec flag on the file descriptor given to a call
   of the form:

       execveat(fd, "", argv, envp, AT_EMPTY_PATH);

   However, the inability to set the close-on-exec flag means that a
   file descriptor referring to the script leaks through to the
   script itself.  As well as wasting a file descriptor, this leakage
   can lead to file-descriptor exhaustion in scenarios where scripts
   recursively employ **execveat**().

SEE ALSO top

   [execve(2)](../man2/execve.2.html), [openat(2)](../man2/openat.2.html), [fexecve(3)](../man3/fexecve.3.html)

COLOPHON top

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Linux man-pages 6.10 2024-07-23 execveat(2)


Pages that refer to this page:execve(2), fanotify_mark(2), open(2), syscalls(2), exec(3), fexecve(3)