EXECVE(2) COMMAND REFERENCE EXECVE(2)
NAME
execve - execute a file
SYNOPSIS
execve(path, argv, envp)
char *path, *argv[], *envp[];
DESCRIPTION
The execve command transforms the calling process into a new
process. The new process is constructed from path, an
ordinary file called the new process file; this file is
either an executable object file, or a file of data for an
interpreter. An executable object file consists of an
identifying header, followed by pages of data representing
the initial program (text) and initialized data pages.
Additional pages may be specified by the header to be
initialized with zero data. See a.out(5).
An interpreter file begins with a line of the form ``#!
interpreter''. The length of this line cannot exceed
SHSIZE, defined in <sys/user.h> (currently 32). When an
interpreter file is execve'd, the system execve's the
specified interpreter. The original arguments are passed to
the interpreter as one argument (arg 1) and path, the name
of the originally execve'd file, is passed as an additional
argument (arg 2).
There can be no return from a successful execve because the
calling core image is lost. This is the mechanism whereby
different process images become active.
The argument argv is an array of character pointers to
null-terminated character strings; these strings constitute
the argument list to be made available to the new process.
By convention, at least one argument must be present in this
array, and the first element of this array should be the
name of the executed program (i.e. the last component of
path).
The argument envp is also an array of character pointers to
null-terminated strings; these strings pass information to
the new process which are not directly arguments to the
command. See environ(7).
Descriptors open in the calling process remain open in the
new process, except for those for which the close-on-exec
flag is set; see close(2). Descriptors which remain open
are unaffected by execve.
Ignored signals remain ignored across an execve, but signals
that are caught are reset to their default values. The
signal stack is reset to be undefined; see sigvec(2) for
Printed 4/6/89 1
EXECVE(2) COMMAND REFERENCE EXECVE(2)
more information.
Each process has real user and group IDs and effective user
and group IDs. The real ID identifies the person using the
system; the effective ID determines his or her access
privileges. The execve command changes the effective user
and group ID to the owner of the executed file if the file
has the "set-user-ID" or "set-group-ID" modes; the real user
ID is not affected.
The new process also inherits the following attributes from
the calling process:
process ID see getpid(2)
parent process IDsee getppid(2)
process group ID see getpgrp(2)
access groups see getgroups(2)
working directorysee chdir(2)
root directory see chroot(2)
control terminal see tty(2)
resource usages see getrusage(2)
interval timers see getitimer(2)
resource limits see getrlimit(2)
file mode mask see umask(2)
signal mask see sigvec(2)
When a "C" program is executed as a result of the call, it
is called as follows:
main(argc, argv, envp)
int argc;
char **argv, **envp;
where argc is the number of elements in argv (the ``arg
count'') and argv is the array of character pointers to the
arguments themselves.
The argument envp is a pointer to an array of strings that
constitute the environment of the process. A pointer to
this array is also stored in the global variable
``environ''. Each string consists of a name, an "=", and a
null-terminated value. The array of pointers is terminated
by a null pointer. The shell sh(1sh) passes an environment
entry for each global shell variable defined when the
program is called. See environ(7) for some conventionally
used names.
DIAGNOSTICS
The execve command fails and returns to the calling process
if one or more of the following are true:
[ENAMETOOLONG]
Printed 4/6/89 2
EXECVE(2) COMMAND REFERENCE EXECVE(2)
The new process file's path name is too long.
[ENOENT] One or more components of the new process file's
path name do not exist, or the interpreter to be
used to execute the new process file does not
exist.
[ENOTDIR] A component of the new process file's or the
interpreter's path name is not a directory.
[EACCES] Search permission is denied for a directory listed
in the new process file's or the interpreter's
path prefix.
[EACCES] The new process file or the interpreter is not an
ordinary file.
[EACCES] The new process file mode or the interpreter mode
denies execute permission.
[ENOEXEC] The new process file or the interpreter has the
appropriate access permission, but has an invalid
magic number in its header (see a.out(5)).
[ETXTBSY] The new process file or the interpreter is a pure
procedure (shared text) file that is currently
open for writing or reading by some process.
[ENOMEM] The new process requires more virtual memory than
is allowed by the imposed maximum (getrlimit(2)).
[E2BIG] The number of bytes in the new process's argument
list is larger than the system-imposed limit of
NCARGS, defined in <sys/param.h>.
[ENOEXEC] The new process file is not as long as indicated
by the size values in its header.
[ENOEXEC] The interpreter name is longer than SHSIZE,
defined in <sys/user.h>.
[EIO] An I/O error occurred while reading from or
writing to the file system.
[EFAULT] Each path, argv, or envp point to an illegal
address.
[ENOMEM] Swap space is not available for the new process,
or the new process file's text size, data size or
stack size exceed the system-imposed limits
MAXTSIZ, MAXDSIZ or MAXSSIZ, defined in
<machine/vmparam.h>.
Printed 4/6/89 3
EXECVE(2) COMMAND REFERENCE EXECVE(2)
RETURN VALUE
If execve returns to the calling process an error has
occurred; the return value will be -1 and the global
variable errno will contain an error code.
CAVEATS
If a program is setuid to a non-superuser, but is executed
when the real uid is ``root'', then the program has the
powers of a superuser as well.
SEE ALSO
close(2), exit(2), fork(2), getrlimit(2), sigvec(2),
execl(3c), a.out(5), and environ(7).
Printed 4/6/89 4
%%index%%
na:288,75;
sy:363,635;
de:998,2903;4261,2260;
di:6521,315;7196,2238;
rv:9794,359;
ca:10153,258;
se:10411,324;
%%index%%000000000143