1EXECVEAT(2) Linux Programmer's Manual EXECVEAT(2)
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6 execveat - execute program relative to a directory file descriptor
7
9 #include <linux/fcntl.h> /* Definition of AT_* constants */
10 #include <unistd.h>
11 int execveat(int dirfd, const char *pathname,
13 const char *const argv[], const char *const envp[],
14 int flags);
15
17 The execveat() system call executes the program referred to by the com‐
18 bination of dirfd and pathname. It operates in exactly the same way as
19 execve(2), except for the differences described in this manual page.
20 If the pathname given in pathname is relative, then it is interpreted
22 relative to the directory referred to by the file descriptor dirfd
23 (rather than relative to the current working directory of the calling
24 process, as is done by execve(2) for a relative pathname).
25 If pathname is relative and dirfd is the special value AT_FDCWD, then
27 pathname is interpreted relative to the current working directory of
28 the calling process (like execve(2)).
29 If pathname is absolute, then dirfd is ignored.
31 If pathname is an empty string and the AT_EMPTY_PATH flag is specified,
33 then the file descriptor dirfd specifies the file to be executed (i.e.,
34 dirfd refers to an executable file, rather than a directory).
35 The flags argument is a bit mask that can include zero or more of the
37 following flags:
38 AT_EMPTY_PATH
40 If pathname is an empty string, operate on the file referred to
41 by dirfd (which may have been obtained using the open(2) O_PATH
42 flag).
43 AT_SYMLINK_NOFOLLOW
45 If the file identified by dirfd and a non-NULL pathname is a
46 symbolic link, then the call fails with the error ELOOP.
47
49 On success, execveat() does not return. On error, -1 is returned, and
50 errno is set to indicate the error.
51
53 The same errors that occur for execve(2) can also occur for execveat().
54 The following additional errors can occur for execveat():
55 EBADF dirfd is not a valid file descriptor.
57 EINVAL Invalid flag specified in flags.
59 ELOOP flags includes AT_SYMLINK_NOFOLLOW and the file identified by
61 dirfd and a non-NULL pathname is a symbolic link.
62 ENOENT The program identified by dirfd and pathname requires the use of
64 an interpreter program (such as a script starting with "#!"),
65 but the file descriptor dirfd was opened with the O_CLOEXEC
66 flag, with the result that the program file is inaccessible to
67 the launched interpreter. See BUGS.
68 ENOTDIR
70 pathname is relative and dirfd is a file descriptor referring to
71 a file other than a directory.
72
74 execveat() was added to Linux in kernel 3.19. Library support was
75 added to glibc in version 2.34.
76
78 The execveat() system call is Linux-specific.
79
81 In addition to the reasons explained in openat(2), the execveat() sys‐
82 tem call is also needed to allow fexecve(3) to be implemented on sys‐
83 tems that do not have the /proc filesystem mounted.
84 When asked to execute a script file, the argv[0] that is passed to the
86 script interpreter is a string of the form /dev/fd/N or /dev/fd/N/P,
87 where N is the number of the file descriptor passed via the dirfd argu‐
88 ment. A string of the first form occurs when AT_EMPTY_PATH is em‐
89 ployed. A string of the second form occurs when the script is speci‐
90 fied via both dirfd and pathname; in this case, P is the value given in
91 pathname.
92 For the same reasons described in fexecve(3), the natural idiom when
94 using execveat() is to set the close-on-exec flag on dirfd. (But see
95 BUGS.)
96
98 The ENOENT error described above means that it is not possible to set
99 the close-on-exec flag on the file descriptor given to a call of the
100 form:
101 execveat(fd, "", argv, envp, AT_EMPTY_PATH);
103 However, the inability to set the close-on-exec flag means that a file
105 descriptor referring to the script leaks through to the script itself.
106 As well as wasting a file descriptor, this leakage can lead to file-de‐
107 scriptor exhaustion in scenarios where scripts recursively employ ex‐
108 ecveat().
109
111 execve(2), openat(2), fexecve(3)
112
114 This page is part of release 5.12 of the Linux man-pages project. A
115 description of the project, information about reporting bugs, and the
116 latest version of this page, can be found at
117 https://www.kernel.org/doc/man-pages/.
118Linux 2021-03-22 EXECVEAT(2)