EXECVE(2)EXECVE(2)NAME
execve, execv - execute a file
SYNOPSIS
int execve(const char*path, char *const argv[], char *const envp);
int execv(const char*path, char *const argv[]);
extern char **environ;
DESCRIPTION
The execve and execv functions transform the calling process into a new
process. The new process is constructed from 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''.
When an interpreter file is exec'd, the system runs the specified
interpreter,giving it the name of the originally
exec'dfileasanargumentand shifting over the rest of the original
arguments.
There can be no return from a successful or execv, since the calling
core image is lost. This is the mechanism whereby different process
images become active.
The argument argv is a null-terminated 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 (that
is, the last component of path).
The execve function takes an additional argument envp which is a null-
terminated array of character pointers to null-terminated strings.
These strings pass information to the new process that is not directly
an argument 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
fcntl(2)). Descriptors that remain open are unaffected by execve or
execv.
Directory streams open in the calling process image are closed in the
new process image.
Ignored signals remain ignored across an execve or execv, but signals
that are caught are reset to their default values. Blocked signals
remain blocked regardless of changes to the signal action. The signal
stack is reset to be undefined (see sigvec(2) for 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 access privileges. The execve and execv functions
change 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 effective user ID and effective
group ID of the new process image will be saved (as the saved set-user-
ID and the saved set-group-ID) for use by the setuid(2)function.
The new process also inherits the following attributes from the calling
process:
process ID see getpid(2)
parent process ID see getppid(2)
process group ID see getpgrp(2)
session membership see setsid(2)
real user ID see getuid(2)
real group ID see getgid(2)
supplementary group IDs see getgroups(2)
time left until an alarm clock signalsee getitimer(2)
current working directory see getwd(3) or getcwd(3P)
root directory see chroot(2)
file mode mask see umask(2)
signal mask see sigprocmask(2)
pending signals see sigpending(2)
tms_utime, tms_stime, tms_cutime, tms_cstimesee times(2)
controlling terminal see tty(4)
resource usages see getrusage(2)
resource limits see getrlimit(2)
When the executed program begins, it is called as follows:
main(int argc, char *argv);
where argc is the number of elements in argv (the ``arg count'') and
argv is the array of character pointers to the arguments themselves.
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(1) passes an environment entry for
each global shell variable defined when the program is called. See
environ(7) for some conventionally used names.
RETURN VALUE
If execve or execv 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.
ERRORS
The execve and execv functions will fail and return to the calling
process if one or more of the following are true:
[ENOTDIR] A component of the path prefix is not a directory.
[EINVAL] The pathname contains a character with the high-order
bit set.
[ENAMETOOLONG] A component of path exceeds 255 characters, or the
entire pathname exceeds 1023 characters. For POSIX
applications these values are given by the constants
{NAME_MAX} and {PATH_MAX}, respectively.
[ENOENT] The new process file does not exist or path points to an
empty string.
[ELOOP] Too many symbolic links were encountered in translating
the pathname.
[EACCES] Search permission is denied for a component of the path
prefix.
[EACCES] The new process file is not an ordinary file.
[EACCES] The new process file mode denies execute permission.
[ENOEXEC] The new process file has the appropriate access
permission, but has an invalid magic number in its
header.
[ETXTBSY] The new process file is a pure procedure (shared text)
file that is currently open for writing or reading by
some process.
[E2BIG] The number of bytes in the new process's argument list
is larger than the system-imposed limit. The limit in
the system as released is 20480 bytes (NCARGS in
<sys/param.h>.
[EFAULT] The new process file is not as long as indicated by the
size values in its header.
[EFAULT] path, argv, or envp point to an illegal address.
[EIO] An I/O error occurred while reading from the file
system.
CAVEATS
If a program is setuid to a non-super-user, but is executed when the
real uid is ``root'', then the program has some of the powers of a
super-user as well.
SEE ALSOexit(2), fork(2), execl(3P), environ(7)
August 1, 1992 EXECVE(2)