1EXEC(3) Linux Programmer's Manual EXEC(3)
2
6 execl, execlp, execle, execv, execvp, execvpe - execute a file
7
9 #include <unistd.h>
10 extern char **environ;
12 int execl(const char *pathname, const char *arg, ...
14 /* (char *) NULL */);
15 int execlp(const char *file, const char *arg, ...
16 /* (char *) NULL */);
17 int execle(const char *pathname, const char *arg, ...
18 /*, (char *) NULL, char *const envp[] */);
19 int execv(const char *pathname, char *const argv[]);
20 int execvp(const char *file, char *const argv[]);
21 int execvpe(const char *file, char *const argv[],
22 char *const envp[]);
23 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
25 execvpe(): _GNU_SOURCE
27
29 The exec() family of functions replaces the current process image with
30 a new process image. The functions described in this manual page are
31 layered on top of execve(2). (See the manual page for execve(2) for
32 further details about the replacement of the current process image.)
33 The initial argument for these functions is the name of a file that is
35 to be executed.
36 The functions can be grouped based on the letters following the "exec"
38 prefix.
39 l - execl(), execlp(), execle()
41 The const char *arg and subsequent ellipses can be thought of as arg0,
42 arg1, ..., argn. Together they describe a list of one or more pointers
43 to null-terminated strings that represent the argument list available
44 to the executed program. The first argument, by convention, should
45 point to the filename associated with the file being executed. The
46 list of arguments must be terminated by a null pointer, and, since
47 these are variadic functions, this pointer must be cast (char *) NULL.
48 By contrast with the 'l' functions, the 'v' functions (below) specify
50 the command-line arguments of the executed program as a vector.
51 v - execv(), execvp(), execvpe()
53 The char *const argv[] argument is an array of pointers to null-termi‐
54 nated strings that represent the argument list available to the new
55 program. The first argument, by convention, should point to the file‐
56 name associated with the file being executed. The array of pointers
57 must be terminated by a null pointer.
58 e - execle(), execvpe()
60 The environment of the caller is specified via the argument envp. The
61 envp argument is an array of pointers to null-terminated strings and
62 must be terminated by a null pointer.
63 All other exec() functions (which do not include 'e' in the suffix)
65 take the environment for the new process image from the external vari‐
66 able environ in the calling process.
67 p - execlp(), execvp(), execvpe()
69 These functions duplicate the actions of the shell in searching for an
70 executable file if the specified filename does not contain a slash (/)
71 character. The file is sought in the colon-separated list of directory
72 pathnames specified in the PATH environment variable. If this variable
73 isn't defined, the path list defaults to a list that includes the di‐
74 rectories returned by confstr(_CS_PATH) (which typically returns the
75 value "/bin:/usr/bin") and possibly also the current working directory;
76 see NOTES for further details.
77 If the specified filename includes a slash character, then PATH is ig‐
79 nored, and the file at the specified pathname is executed.
80 In addition, certain errors are treated specially.
82 If permission is denied for a file (the attempted execve(2) failed with
84 the error EACCES), these functions will continue searching the rest of
85 the search path. If no other file is found, however, they will return
86 with errno set to EACCES.
87 If the header of a file isn't recognized (the attempted execve(2)
89 failed with the error ENOEXEC), these functions will execute the shell
90 (/bin/sh) with the path of the file as its first argument. (If this
91 attempt fails, no further searching is done.)
92 All other exec() functions (which do not include 'p' in the suffix)
94 take as their first argument a (relative or absolute) pathname that
95 identifies the program to be executed.
96
98 The exec() functions return only if an error has occurred. The return
99 value is -1, and errno is set to indicate the error.
100
102 All of these functions may fail and set errno for any of the errors
103 specified for execve(2).
104
106 The execvpe() function first appeared in glibc 2.11.
107
109 For an explanation of the terms used in this section, see at‐
110 tributes(7).
111 ┌──────────────────────────────┬───────────────┬─────────────┐
113 │Interface │ Attribute │ Value │
114 ├──────────────────────────────┼───────────────┼─────────────┤
115 │execl(), execle(), execv() │ Thread safety │ MT-Safe │
116 ├──────────────────────────────┼───────────────┼─────────────┤
117 │execlp(), execvp(), execvpe() │ Thread safety │ MT-Safe env │
118 └──────────────────────────────┴───────────────┴─────────────┘
120 POSIX.1-2001, POSIX.1-2008.
121 The execvpe() function is a GNU extension.
123
125 The default search path (used when the environment does not contain the
126 variable PATH) shows some variation across systems. It generally in‐
127 cludes /bin and /usr/bin (in that order) and may also include the cur‐
128 rent working directory. On some other systems, the current working is
129 included after /bin and /usr/bin, as an anti-Trojan-horse measure. The
130 glibc implementation long followed the traditional default where the
131 current working directory is included at the start of the search path.
132 However, some code refactoring during the development of glibc 2.24
133 caused the current working directory to be dropped altogether from the
134 default search path. This accidental behavior change is considered
135 mildly beneficial, and won't be reverted.
136 The behavior of execlp() and execvp() when errors occur while attempt‐
138 ing to execute the file is historic practice, but has not traditionally
139 been documented and is not specified by the POSIX standard. BSD (and
140 possibly other systems) do an automatic sleep and retry if ETXTBSY is
141 encountered. Linux treats it as a hard error and returns immediately.
142 Traditionally, the functions execlp() and execvp() ignored all errors
144 except for the ones described above and ENOMEM and E2BIG, upon which
145 they returned. They now return if any error other than the ones de‐
146 scribed above occurs.
147
149 Before glibc 2.24, execl() and execle() employed realloc(3) internally
150 and were consequently not async-signal-safe, in violation of the re‐
151 quirements of POSIX.1. This was fixed in glibc 2.24.
152 Architecture-specific details
154 On sparc and sparc64, execv() is provided as a system call by the ker‐
155 nel (with the prototype shown above) for compatibility with SunOS.
156 This function is not employed by the execv() wrapper function on those
157 architectures.
158
160 sh(1), execve(2), execveat(2), fork(2), ptrace(2), fexecve(3), sys‐
161 tem(3), environ(7)
162
164 This page is part of release 5.10 of the Linux man-pages project. A
165 description of the project, information about reporting bugs, and the
166 latest version of this page, can be found at
167 https://www.kernel.org/doc/man-pages/.
168GNU 2019-08-02 EXEC(3)