.\" Copyright (c) 2014 Google, Inc., written by David Drysdale .\" and Copyright (c) 2015, Michael Kerrisk .\" .\" %%%LICENSE_START(VERBATIM) .\" 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 .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date.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. .\" %%%LICENSE_END .\" .TH EXECVEAT 2 2017-09-15 "Linux" "Linux Programmer's Manual" .SH NAME execveat \- execute program relative to a directory file descriptor .SH SYNOPSIS .B #include .PP .BI "int execveat(int " dirfd ", const char *" pathname "," .br .BI " char *const " argv "[], char *const " envp "[]," .br .BI " int " flags ); .SH DESCRIPTION .\" commit 51f39a1f0cea1cacf8c787f652f26dfee9611874 The .BR execveat () system call executes the program referred to by the combination of .I dirfd and .IR pathname . It operates in exactly the same way as .BR execve (2), except for the differences described in this manual page. .PP If the pathname given in .I pathname is relative, then it is interpreted relative to the directory referred to by the file descriptor .I dirfd (rather than relative to the current working directory of the calling process, as is done by .BR execve (2) for a relative pathname). .PP If .I pathname is relative and .I dirfd is the special value .BR AT_FDCWD , then .I pathname is interpreted relative to the current working directory of the calling process (like .BR execve (2)). .PP If .I pathname is absolute, then .I dirfd is ignored. .PP If .I pathname is an empty string and the .BR AT_EMPTY_PATH flag is specified, then the file descriptor .I dirfd specifies the file to be executed (i.e., .IR dirfd refers to an executable file, rather than a directory). .PP The .I flags argument is a bit mask that can include zero or more of the following flags: .TP .BR AT_EMPTY_PATH If .I pathname is an empty string, operate on the file referred to by .IR dirfd (which may have been obtained using the .BR open (2) .B O_PATH flag). .TP .B AT_SYMLINK_NOFOLLOW If the file identified by .I dirfd and a non-NULL .I pathname is a symbolic link, then the call fails with the error .BR ELOOP . .SH RETURN VALUE On success, .BR execveat () does not return. On error, \-1 is returned, and .I errno is set appropriately. .SH ERRORS The same errors that occur for .BR execve (2) can also occur for .BR execveat (). The following additional errors can occur for .BR execveat (): .TP .B EBADF .I dirfd is not a valid file descriptor. .TP .B EINVAL Invalid flag specified in .IR flags . .TP .B ELOOP .I flags includes .BR AT_SYMLINK_NOFOLLOW and the file identified by .I dirfd and a non-NULL .I pathname is a symbolic link. .TP .B ENOENT The program identified by .I dirfd and .I pathname requires the use of an interpreter program (such as a script starting with "#!"), but the file descriptor .I dirfd was opened with the .B O_CLOEXEC flag, with the result that the program file is inaccessible to the launched interpreter. See BUGS. .TP .B ENOTDIR .I pathname is relative and .I dirfd is a file descriptor referring to a file other than a directory. .SH VERSIONS .BR execveat () was added to Linux in kernel 3.19. GNU C library support is pending. .\" FIXME . check for glibc support in a future release .SH CONFORMING TO The .BR execveat () system call is Linux-specific. .SH NOTES In addition to the reasons explained in .BR openat (2), the .BR execveat () system call is also needed to allow .BR fexecve (3) to be implemented on systems that do not have the .I /proc filesystem mounted. .PP When asked to execute a script file, the .IR argv[0] that is passed to the script interpreter is a string of the form .IR /dev/fd/N or .IR /dev/fd/N/P , where .I N is the number of the file descriptor passed via the .IR dirfd argument. A string of the first form occurs when .BR AT_EMPTY_PATH is employed. A string of the second form occurs when the script is specified via both .IR dirfd and .IR pathname ; in this case, .IR P is the value given in .IR pathname . .PP For the same reasons described in .BR fexecve (3), the natural idiom when using .BR execveat () is to set the close-on-exec flag on .IR dirfd . (But see BUGS.) .SH BUGS The .B 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: .PP execveat(fd, "", argv, envp, AT_EMPTY_PATH); .PP 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 .BR execveat (). .\" For an example, see Michael Kerrisk's 2015-01-10 reply in this LKML .\" thread (http://thread.gmane.org/gmane.linux.kernel/1836105/focus=20229): .\" .\" Subject: [PATCHv10 man-pages 5/5] execveat.2: initial man page.\" for execveat(2 .\" Date: Mon, 24 Nov 2014 11:53:59 +0000 .SH SEE ALSO .BR execve (2), .BR openat (2), .BR fexecve (3) .SH COLOPHON This page is part of release 5.10 of the Linux .I man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at \%https://www.kernel.org/doc/man\-pages/.