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)