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28 .\" @(#)execve.2 8.5 (Berkeley) 6/1/94
42 .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.
58 Additional pages may be specified
59 by the header to be initialized with zero data; see
64 An interpreter file begins with a line of the form:
66 .Bd -ragged -offset indent -compact
72 When an interpreter file is
80 is specified, it becomes the first argument to the
82 and the name of the originally
84 file becomes the second argument;
85 otherwise, the name of the originally
87 file becomes the first argument.
88 The original arguments are shifted over to
89 become the subsequent arguments.
90 The zeroth argument is set to the specified
95 is a pointer to a null-terminated array of
96 character pointers to null-terminated character strings.
97 These strings construct the argument list to be made available to the new
99 At least one argument must be present in
100 the array; by custom, the first element should be
101 the name of the executed program (for example, the last component of
106 is also a pointer to a null-terminated array of
107 character pointers to null-terminated strings.
108 A pointer to this array is normally stored in the global variable
110 These strings pass information to the
111 new process that is not directly an argument to the command (see
114 File descriptors open in the calling process image remain open in
115 the new process image, except for those for which the close-on-exec
120 Descriptors that remain open are unaffected by
122 If any of the standard descriptors (0, 1, and/or 2) are closed at the
125 is called, and the process will gain privilege as a result of set-id
126 semantics, those descriptors will be re-opened automatically.
127 No programs, whether privileged or not, should assume that these descriptors
128 will remain closed across a call to
131 Signals set to be ignored in the calling process are set to be ignored in
134 Signals which are set to be caught in the calling process image
135 are set to default action in the new process image.
136 Blocked signals remain blocked regardless of changes to the signal action.
137 The signal stack is reset to be undefined (see
139 for more information).
141 If the set-user-ID mode bit of the new process image file is set
144 the effective user ID of the new process image is set to the owner ID
145 of the new process image file.
146 If the set-group-ID mode bit of the new process image file is set,
147 the effective group ID of the new process image is set to the group ID
148 of the new process image file.
149 (The effective group ID is the first element of the group list.)
150 The real user ID, real group ID and
151 other group IDs of the new process image remain the same as the calling
153 After any set-user-ID and set-group-ID processing,
154 the effective user ID is recorded as the saved set-user-ID,
155 and the effective group ID is recorded as the saved set-group-ID.
156 These values may be used in changing the effective IDs later (see
159 The set-ID bits are not honored if the respective file system has the
161 option enabled or if the new process file is an interpreter file.
163 tracing is disabled if effective IDs are changed.
165 The new process also inherits the following attributes from
168 .Bl -column parent_process_ID -offset indent -compact
169 .It process ID Ta see Xr getpid 2
170 .It parent process ID Ta see Xr getppid 2
171 .It process group ID Ta see Xr getpgrp 2
172 .It access groups Ta see Xr getgroups 2
173 .It working directory Ta see Xr chdir 2
174 .It root directory Ta see Xr chroot 2
175 .It control terminal Ta see Xr termios 4
176 .It resource usages Ta see Xr getrusage 2
177 .It interval timers Ta see Xr getitimer 2
178 .It resource limits Ta see Xr getrlimit 2
179 .It file mode mask Ta see Xr umask 2
180 .It signal mask Ta see Xr sigvec 2 ,
184 When a program is executed as a result of an
186 system call, it is entered as follows:
187 .Bd -literal -offset indent
188 main(argc, argv, envp)
195 is the number of elements in
200 points to the array of character pointers
201 to the arguments themselves.
205 system call overlays the current process image
206 with a new process image the successful call
207 has no process to return to.
210 does return to the calling process an error has occurred; the
211 return value will be -1 and the global variable
213 is set to indicate the error.
218 will fail and return to the calling process if:
221 A component of the path prefix is not a directory.
222 .It Bq Er ENAMETOOLONG
223 A component of a pathname exceeded 255 characters,
224 or an entire path name exceeded 1023 characters.
225 .It Bq Er ENAMETOOLONG
226 When invoking an interpreted script, the interpreter name
231 The new process file does not exist.
233 Too many symbolic links were encountered in translating the pathname.
235 Search permission is denied for a component of the path prefix.
237 The new process file is not an ordinary file.
239 The new process file mode denies execute permission.
241 The new process file has the appropriate access
242 permission, but has an invalid magic number in its header.
244 The new process file is a pure procedure (shared text)
245 file that is currently open for writing or reading by some process.
247 The new process requires more virtual memory than
248 is allowed by the imposed maximum
251 The number of bytes in the new process' argument list
252 is larger than the system-imposed limit.
253 This limit is specified by the
258 The new process file is not as long as indicated by
259 the size values in its header.
268 to an illegal address.
270 An I/O error occurred while reading from the file system.
275 to a non-super-user, but is executed when
278 is ``root'', then the program has some of the powers
279 of a super-user as well.
294 system call conforms to
296 with the exception of reopening descriptors 0, 1, and/or 2 in certain
298 A future update of the Standard is expected to require this behavior,
299 and it may become the default for non-privileged processes as well.
300 .\" NB: update this caveat when TC1 is blessed.
301 The support for executing interpreted programs is an extension.
305 system call appeared in