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32 .\" @(#)execve.2 8.5 (Berkeley) 6/1/94
42 .Fd #include <unistd.h>
44 .Fn execve "const char *path" "char *const argv[]" "char *const envp[]"
47 transforms the calling process into a new process.
48 The new process is constructed from an ordinary file,
49 whose name is pointed to by
52 .Em new process file .
53 This file is either an executable object file,
54 or a file of data for an interpreter.
55 An executable object file consists of an identifying header,
56 followed by pages of data representing the initial program (text)
57 and initialized data pages. Additional pages may be specified
58 by the header to be initialized with zero data; see
61 An interpreter file begins with a line of the form:
63 .Bd -filled -offset indent -compact
69 When an interpreter file is
77 is specified, it becomes the first argument to the
79 and the name of the originally
81 file becomes the second argument;
82 otherwise, the name of the originally
84 file becomes the first argument. The original arguments are shifted over to
85 become the subsequent arguments. The zeroth argument, normally the name of the
87 file, is left unchanged.
91 is a pointer to a null-terminated array of
92 character pointers to null-terminated character strings.
93 These strings construct the argument list to be made available to the new
94 process. At least one argument must be present in
95 the array; by custom, the first element should be
96 the name of the executed program (for example, the last component of
101 is also a pointer to a null-terminated array of
102 character pointers to null-terminated strings.
103 A pointer to this array is normally stored in the global variable
105 These strings pass information to the
106 new process that is not directly an argument to the command (see
109 File descriptors open in the calling process image remain open in
110 the new process image, except for those for which the close-on-exec
115 Descriptors that remain open are unaffected by
118 Signals set to be ignored in the calling process are set to be ignored in
120 new process. Signals which are set to be caught in the calling process image
121 are set to default action in the new process image.
122 Blocked signals remain blocked regardless of changes to the signal action.
123 The signal stack is reset to be undefined (see
125 for more information).
127 If the set-user-ID mode bit of the new process image file is set
130 the effective user ID of the new process image is set to the owner ID
131 of the new process image file.
132 If the set-group-ID mode bit of the new process image file is set,
133 the effective group ID of the new process image is set to the group ID
134 of the new process image file.
135 (The effective group ID is the first element of the group list.)
136 The real user ID, real group ID and
137 other group IDs of the new process image remain the same as the calling
139 After any set-user-ID and set-group-ID processing,
140 the effective user ID is recorded as the saved set-user-ID,
141 and the effective group ID is recorded as the saved set-group-ID.
142 These values may be used in changing the effective IDs later (see
146 The set-ID bits are not honored if the respective file system has the
148 option enabled or if the new process file is an interpreter file. Syscall
149 tracing is disabled if effective IDs are changed.
151 The new process also inherits the following attributes from
154 .Bl -column parent_process_ID -offset indent -compact
155 .It process ID Ta see Xr getpid 2
156 .It parent process ID Ta see Xr getppid 2
157 .It process group ID Ta see Xr getpgrp 2
158 .It access groups Ta see Xr getgroups 2
159 .It working directory Ta see Xr chdir 2
160 .It root directory Ta see Xr chroot 2
161 .It control terminal Ta see Xr termios 4
162 .It resource usages Ta see Xr getrusage 2
163 .It interval timers Ta see Xr getitimer 2
164 .It resource limits Ta see Xr getrlimit 2
165 .It file mode mask Ta see Xr umask 2
166 .It signal mask Ta see Xr sigvec 2 ,
170 When a program is executed as a result of an
172 call, it is entered as follows:
173 .Bd -literal -offset indent
174 main(argc, argv, envp)
181 is the number of elements in
186 points to the array of character pointers
187 to the arguments themselves.
188 .Sh IMPLEMENTATION NOTES
190 In the non-threaded library
192 is implemented as the
196 In the threaded library, the
198 syscall is assembled to
199 .Fn _thread_sys_execve
202 is implemented as a function which performs user-thread
203 library re-initialization and then calls
204 .Fn _thread_sys_execve .
208 function overlays the current process image
209 with a new process image the successful call
210 has no process to return to.
213 does return to the calling process an error has occurred; the
214 return value will be -1 and the global variable
216 is set to indicate the error.
219 will fail and return to the calling process if:
220 .Bl -tag -width [ENAMETOOLONG]
222 A component of the path prefix is not a directory.
223 .It Bq Er ENAMETOOLONG
224 A component of a pathname exceeded 255 characters,
225 or an entire path name exceeded 1023 characters.
227 The new process file does not exist.
229 Too many symbolic links were encountered in translating the pathname.
231 Search permission is denied for a component of the path prefix.
233 The new process file is not an ordinary file.
235 The new process file mode denies execute permission.
237 The new process file has the appropriate access
238 permission, but has an invalid magic number in its header.
240 The new process file is a pure procedure (shared text)
241 file that is currently open for writing or reading by some process.
244 The new process requires more virtual memory than
245 is allowed by the imposed maximum
248 The number of bytes in the new process' argument list
249 is larger than the system-imposed limit.
250 This limit is specified by the
255 The new process file is not as long as indicated by
256 the size values in its header.
263 to an illegal address.
265 An I/O error occurred while reading from the file system.
270 to a non-super-user, but is executed when
273 is ``root'', then the program has some of the powers
274 of a super-user as well.
287 function call appeared in