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28 .\" @(#)execve.2 8.5 (Berkeley) 6/1/94
29 .\" $FreeBSD: src/lib/libc/sys/execve.2,v 1.16.2.10 2001/12/22 01:21:30 jwd Exp $
43 .Fn execve "const char *path" "char *const argv[]" "char *const envp[]"
45 .Fn fexecve "int fd" "char *const argv[]" "char *const envp[]"
48 transforms the calling process into a new process.
49 The new process is constructed from an ordinary file,
50 whose name is pointed to by
53 .Em new process file .
56 system call is equivalent to
58 except that the file to be executed is determined by the file descriptor
64 is either an executable object file,
65 or a file of data for an interpreter.
66 An executable object file consists of an identifying header,
67 followed by pages of data representing the initial program (text)
68 and initialized data pages.
69 Additional pages may be specified
70 by the header to be initialized with zero data; see
75 An interpreter file begins with a line of the form:
77 .Bd -ragged -offset indent -compact
83 When an interpreter file is
91 is specified, it becomes the first argument to the
93 and the name of the originally
95 file becomes the second argument;
96 otherwise, the name of the originally
98 file becomes the first argument.
99 The original arguments are shifted over to become the subsequent arguments.
100 The zeroth argument is set to the specified
104 for a detailed discussion of interpreter file execution.)
108 is a pointer to a null-terminated array of
109 character pointers to null-terminated character strings.
110 These strings construct the argument list to be made available to the new
112 At least one argument must be present in
113 the array; by custom, the first element should be
114 the name of the executed program (for example, the last component of
119 is also a pointer to a null-terminated array of
120 character pointers to null-terminated strings.
121 A pointer to this array is normally stored in the global variable
123 These strings pass information to the
124 new process that is not directly an argument to the command (see
127 File descriptors open in the calling process image remain open in
128 the new process image, except for those for which the close-on-exec
133 Descriptors that remain open are unaffected by
135 If any of the standard descriptors (0, 1, and/or 2) are closed at the time
137 is called, and the process will gain privilege as a result of set-id
138 semantics, those descriptors will be reopened automatically.
139 No programs, whether privileged or not, should assume that these descriptors
140 will remain closed across a call to
143 Signals set to be ignored in the calling process are set to be ignored in
146 Signals which are set to be caught in the calling process image
147 are set to default action in the new process image.
148 Blocked signals remain blocked regardless of changes to the signal action.
149 The signal stack is reset to be undefined (see
151 for more information).
153 If the set-user-ID mode bit of the new process image file is set
156 the effective user ID of the new process image is set to the owner ID
157 of the new process image file.
158 If the set-group-ID mode bit of the new process image file is set,
159 the effective group ID of the new process image is set to the group ID
160 of the new process image file.
161 (The effective group ID is the first element of the group list.)
162 The real user ID, real group ID and
163 other group IDs of the new process image remain the same as the calling
165 After any set-user-ID and set-group-ID processing,
166 the effective user ID is recorded as the saved set-user-ID,
167 and the effective group ID is recorded as the saved set-group-ID.
168 These values may be used in changing the effective IDs later (see
171 The set-ID bits are not honored if the respective file system has the
173 option enabled or if the new process file is an interpreter file.
174 Syscall tracing is disabled if effective IDs are changed.
176 The new process also inherits the following attributes from
179 .Bl -column parent_process_ID -offset indent -compact
180 .It process ID Ta see Xr getpid 2
181 .It parent process ID Ta see Xr getppid 2
182 .It process group ID Ta see Xr getpgrp 2
183 .It access groups Ta see Xr getgroups 2
184 .It working directory Ta see Xr chdir 2
185 .It root directory Ta see Xr chroot 2
186 .It control terminal Ta see Xr termios 4
187 .It resource usages Ta see Xr getrusage 2
188 .It interval timers Ta see Xr getitimer 2
189 .It resource limits Ta see Xr getrlimit 2
190 .It file mode mask Ta see Xr umask 2
191 .It signal mask Ta see Xr sigaction 2 ,
195 When a program is executed as a result of an
197 call, it is entered as follows:
198 .Bd -literal -offset indent
199 .Fn main "int argc" "char **argv" "char **envp" ;
204 is the number of elements in
210 points to the array of character pointers
211 to the arguments themselves.
215 function ignores the file offset of
217 Since the execute permission is checked by
221 need not have been opened with the
224 However, if the file to be executed denies read permission for the process
225 preparing to do the exec, the only way to provide the
233 Note that the file to be executed can not be open for writing.
237 overlays the current process image
238 with a new process image the successful call
239 has no process to return to.
242 does return to the calling process an error has occurred; the
243 return value will be -1 and the global variable
245 is set to indicate the error.
248 has the same return values as
252 will fail and return to the calling process if:
255 A component of the path prefix is not a directory.
256 .It Bq Er ENAMETOOLONG
257 A component of a pathname exceeded 255 characters,
258 or an entire path name exceeded 1023 characters.
259 .It Bq Er ENAMETOOLONG
260 When invoking an interpreted script, the interpreter name
265 The new process file does not exist.
267 Too many symbolic links were encountered in translating the pathname.
269 Search permission is denied for a component of the path prefix.
271 The new process file is not an ordinary file.
273 The new process file mode denies execute permission.
275 The new process file has the appropriate access
276 permission, but has an invalid magic number in its header.
278 The new process file is a pure procedure (shared text)
279 file that is currently open for writing or reading by some process.
281 The new process requires more virtual memory than
282 is allowed by the imposed maximum
285 The number of bytes in the new process' argument list
286 is larger than the system-imposed limit.
287 This limit is specified by the
292 The new process file is not as long as indicated by
293 the size values in its header.
300 to an illegal address.
302 An I/O error occurred while reading from the file system.
307 system call will fail and return to the calling process if:
312 argument is not a valid file descriptor open for executing.
317 to a non-super-user, but is executed when
322 then the program has some of the powers
323 of a super-user as well.
327 refers to to an interpreter file and the
335 has already been closed by the time the interpreter is executed.
351 system call conforms to
355 system call conforms to
358 The support for executing interpreted programs is an extension.
362 system call appeared in
366 system call first appeared in