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System Calls exec(2)
NAME
exec, execl, execle, execlp, execv, execve, execvp - execute
a file
SYNOPSIS
#include <unistd.h>
int execl(const char *path, const char *arg0, ... /* const
char *argn, (char *)0 */);
int execv(const char *path, char *const argv[]);
int execle(const char *path, const char *arg0, ... /* const
char *argn, (char *)0, char *const envp[]*/);
int execve(const char *path, char *const argv[], char *const
envp[]);
int execlp(const char *file, const char *arg0, ... /* const
char *argn, (char *)0 */);
int execvp(const char *file, char *const argv[]);
DESCRIPTION
Each of the functions in the exec family replaces the
current process image with a new process image. The new
image is constructed from a regular, executable file called
the new process image file. This file is either an execut-
able object file or a file of data for an interpreter. There
is no return from a successful call to one of these func-
tions because the calling process image is overlaid by the
new process image.
An interpreter file begins with a line of the form
#! pathname [arg]
where pathname is the path of the interpreter, and arg is an
optional argument. When an interpreter file is executed, the
system invokes the specified interpreter. The pathname
specified in the interpreter file is passed as arg0 to the
interpreter. If arg was specified in the interpreter file,
it is passed as arg1 to the interpreter. The remaining argu-
ments to the interpreter are arg0 through argn of the origi-
nally exec'd file. The interpreter named by pathname must
not be an interpreter file.
When a C-language program is executed as a result of this
call, it is entered as a C-language function call as fol-
lows:
SunOS 5.10 Last change: 18 Dec 2003 1
System Calls exec(2)
int main (int argc, char *argv[], char *envp[]);
where argc is the argument count, argv is an array of char-
acter pointers to the arguments themselves, and envp is an
array of character pointers to the environment strings. The
argv and environ arrays are each terminated by a null
pointer. The null pointer terminating the argv array is not
counted in argc. The value of argc is non-negative, and if
greater than 0, argv[0] points to a string containing the
name of the file. If argc is 0, argv[0] is a null pointer,
in which case there are no arguments. Applications should
verify that argc is greater than 0 or that argv[0] is not a
null pointer before dereferencing argv[0].
The arguments specified by a program with one of the exec
functions are passed on to the new process image in the
main() arguments.
The path argument points to a path name that identifies the
new process image file.
The file argument is used to construct a pathname that iden-
tifies the new process image file. If the file argument con-
tains a slash character, it is used as the pathname for this
file. Otherwise, the path prefix for this file is obtained
by a search of the directories passed in the PATH environ-
ment variable (see environ(5)). The environment is supplied
typically by the shell. If the process image file is not a
valid executable object file, execlp() and execvp() use the
contents of that file as standard input to the shell. In
this case, the shell becomes the new process image. The
standard to which the caller conforms determines which shell
is used. See standards(5).
The arguments represented by arg0... are pointers to null-
terminated character strings. These strings constitute the
argument list available to the new process image. The list
is terminated by a null pointer. The arg0 argument should
point to a filename that is associated with the process
being started by one of the exec functions.
The argv argument is an array of character pointers to
null-terminated strings. The last member of this array must
be a null pointer. These strings constitute the argument
list available to the new process image. The value in
argv[0] should point to a filename that is associated with
the process being started by one of the exec functions.
The envp argument is an array of character pointers to
null-terminated strings. These strings constitute the
environment for the new process image. The envp array is
SunOS 5.10 Last change: 18 Dec 2003 2
System Calls exec(2)
terminated by a null pointer. For execl(), execv(),
execvp(), and execlp(), the C-language run-time start-off
routine places a pointer to the environment of the calling
process in the global object extern char **environ, and it
is used to pass the environment of the calling process to
the new process image.
The number of bytes available for the new process's combined
argument and environment lists is ARG_MAX. It is
implementation-dependent whether null terminators, pointers,
and/or any alignment bytes are included in this total.
File descriptors open in the calling process image remain
open in the new process image, except for those whose
close-on-exec flag FD_CLOEXEC is set; see fcntl(2). For
those file descriptors that remain open, all attributes of
the open file description, including file locks, remain
unchanged.
The preferred hardware address translation size (see
memcntl(2)) for the stack and heap of the new process image
are set to the default system page size.
Directory streams open in the calling process image are
closed in the new process image.
The state of conversion descriptors and message catalogue
descriptors in the new process image is undefined. For the
new process, the equivalent of:
setlocale(LC_ALL, "C")
is executed at startup.
Signals set to the default action (SIG_DFL) in the calling
process image are set to the default action in the new pro-
cess image (see signal(3C)). Signals set to be ignored
(SIG_IGN) by the calling process image are set to be ignored
by the new process image. Signals set to be caught by the
calling process image are set to the default action in the
new process image (see signal.h(3HEAD)). After a successful
call to any of the exec functions, alternate signal stacks
are not preserved and the SA_ONSTACK flag is cleared for all
signals.
After a successful call to any of the exec functions, any
functions previously registered by atexit(3C) are no longer
registered.
The saved resource limits in the new process image are set
to be a copy of the process's corresponding hard and soft
SunOS 5.10 Last change: 18 Dec 2003 3
System Calls exec(2)
resource limits.
If the ST_NOSUID bit is set for the file system containing
the new process image file, then the effective user ID and
effective group ID are unchanged in the new process image.
If the set-user-ID mode bit of the new process image file is
set (see chmod(2)), the effective user ID of the new process
image is set to the owner ID of the new process image file.
Similarly, if the set-group-ID mode bit of the new process
image file is set, the effective group ID of the new process
image is set to the group ID of the new process image file.
The real user ID and real group ID of the new process image
remain the same as those of the calling process image. The
effective user ID and effective group ID of the new process
image are saved (as the saved set-user-ID and the saved
set-group-ID for use by setuid(2).
The privilege sets are changed according to the following
rules:
1. The inheritable set, I, is intersected with the limit
set, L. This mechanism enforces the limit set for
processes.
2. The effective set, E, and the permitted set, P, are made
equal to the new inheritable set.
The system attempts to set the privilege-aware state to
non-PA both before performing any modifications to the pro-
cess IDs and privilege sets as well as after completing the
transition to new UIDs and privilege sets, following the
rules outlined in privileges(5).
If the {PRIV_PROC_OWNER} privilege is asserted in the effec-
tive set, the set-user-ID and set-group-ID bits will be
honored when the process is being controlled by ptrace(3C).
Additional restriction can apply when the traced process has
an effective UID of 0. See privileges(5).
Any shared memory segments attached to the calling process
image will not be attached to the new process image (see
shmop(2)). Any mappings established through mmap() are not
preserved across an exec. Memory mappings created in the
process are unmapped before the address space is rebuilt for
the new process image. See mmap(2).
Memory locks established by the calling process via calls to
mlockall(3C) or mlock(3C) are removed. If locked pages in
the address space of the calling process are also mapped
into the address spaces the locks established by the other
SunOS 5.10 Last change: 18 Dec 2003 4
System Calls exec(2)
processes will be unaffected by the call by this process to
the exec function. If the exec function fails, the effect on
memory locks is unspecified.
If _XOPEN_REALTIME is defined and has a value other than -1,
any named semaphores open in the calling process are closed
as if by appropriate calls to sem_close(3RT)
Profiling is disabled for the new process; see profil(2).
Timers created by the calling process with timer_create(3RT)
are deleted before replacing the current process image with
the new process image.
For the SCHED_FIFO and SCHED_RR scheduling policies, the
policy and priority settings are not changed by a call to an
exec function.
All open message queue descriptors in the calling process
are closed, as described in mq_close(3RT).
Any outstanding asynchronous I/O operations may be can-
celled. Those asynchronous I/O operations that are not can-
celed will complete as if the exec function had not yet
occurred, but any associated signal notifications are
suppressed. It is unspecified whether the exec function
itself blocks awaiting such I/O completion. In no event,
however, will the new process image created by the exec
function be affected by the presence of outstanding asyn-
chronous I/O operations at the time the exec function is
called.
All active contract templates are cleared (see contract(4)).
The new process also inherits the following attributes from
the calling process:
o nice value (see nice(2))
o scheduler class and priority (see priocntl(2))
o process ID
o parent process ID
o process group ID
o task ID
o supplementary group IDs
o
SunOS 5.10 Last change: 18 Dec 2003 5
System Calls exec(2)
semadj values (see semop(2))
o session membership (see exit(2) and signal(3C))
o real user ID
o real group ID
o project ID
o trace flag (see ptrace(3C) request 0)
o time left until an alarm clock signal (see alarm(2))
o current working directory
o root directory
o file mode creation mask (see umask(2))
o file size limit (see ulimit(2))
o resource limits (see getrlimit(2))
o tms_utime, tms_stime, tms_cutime, and tms_cstime (see
times(2))
o file-locks (see fcntl(2) and lockf(3C))
o controlling terminal
o process signal mask (see sigprocmask(2))
o pending signals (see sigpending(2))
o processor bindings (see processor_bind(2))
o processor set bindings (see pset_bind(2))
o limit privilege set
o privilege debugging flag (see privileges(5) and
getpflags(2))
A call to any exec function from a process with more than
one thread results in all threads being terminated and the
new executable image being loaded and executed. No destruc-
tor functions will be called.
Upon successful completion, each of the functions in the
exec family marks for update the st_atime field of the file.
SunOS 5.10 Last change: 18 Dec 2003 6
System Calls exec(2)
If an exec function failed but was able to locate the pro-
cess image file, whether the st_atime field is marked for
update is unspecified. Should the function succeed, the pro-
cess image file is considered to have been opened with
open(2). The corresponding close(2) is considered to occur
at a time after this open, but before process termination or
successful completion of a subsequent call to one of the
exec functions. The argv[] and envp[] arrays of pointers and
the strings to which those arrays point will not be modified
by a call to one of the exec functions, except as a conse-
quence of replacing the process image.
The saved resource limits in the new process image are set
to be a copy of the process's corresponding hard and soft
limits.
RETURN VALUES
If a function in the exec family returns to the calling pro-
cess image, an error has occurred; the return value is -1
and errno is set to indicate the error.
ERRORS
The exec functions will fail if:
E2BIG The number of bytes in the new process's
argument list is greater than the system-
imposed limit of {ARG_MAX} bytes. The argu-
ment list limit is sum of the size of the
argument list plus the size of the
environment's exported shell variables.
EACCES Search permission is denied for a directory
listed in the new process file's path pre-
fix.
The new process file is not an ordinary
file.
The new process file mode denies execute
permission.
The {FILE_DAC_SEARCH} privilege overrides
the restriction on directory searches.
The {FILE_DAC_EXECUTE} privilege overrides
the lack of execute permission.
SunOS 5.10 Last change: 18 Dec 2003 7
System Calls exec(2)
EAGAIN Total amount of system memory available when
reading using raw I/O is temporarily insuf-
ficient.
EFAULT An argument points to an illegal address.
EINVAL The new process image file has the appropri-
ate permission and has a recognized execut-
able binary format, but the system does not
support execution of a file with this for-
mat.
EINTR A signal was caught during the execution of
one of the functions in the exec family.
ELOOP Too many symbolic links were encountered in
translating path or file.
ENAMETOOLONG The length of the file or path argument
exceeds {PATH_MAX}, or the length of a file
or path component exceeds {NAME_MAX} while
{_POSIX_NO_TRUNC} is in effect.
ENOENT One or more components of the new process
path name of the file do not exist or is a
null pathname.
ENOLINK The path argument points to a remote machine
and the link to that machine is no longer
active.
ENOTDIR A component of the new process path of the
file prefix is not a directory.
SunOS 5.10 Last change: 18 Dec 2003 8
System Calls exec(2)
The exec functions, except for execlp() and execvp(), will
fail if:
ENOEXEC The new process image file has the
appropriate access permission but is
not in the proper format.
The exec functions may fail if:
ENAMETOOLONG Pathname resolution of a symbolic link pro-
duced an intermediate result whose length
exceeds {PATH_MAX}.
ENOMEM The new process image requires more memory
than is allowed by the hardware or system-
imposed by memory management constraints.
See brk(2).
ETXTBSY The new process image file is a pure pro-
cedure (shared text) file that is currently
open for writing by some process.
USAGE
As the state of conversion descriptors and message catalogue
descriptors in the new process image is undefined, portable
applications should not rely on their use and should close
them prior to calling one of the exec functions.
Applications that require other than the default POSIX
locale should call setlocale(3C) with the appropriate param-
eters to establish the locale of thenew process.
The environ array should not be accessed directly by the
application.
ATTRIBUTES
See attributes(5) for descriptions of the following attri-
butes:
SunOS 5.10 Last change: 18 Dec 2003 9
System Calls exec(2)
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Standard |
|_____________________________|_____________________________|
| MT-Level | See below. |
|_____________________________|_____________________________|
The execle() and execve() fucntions are Async-Signal-Safe.
SEE ALSO
ksh(1), ps(1), sh(1), alarm(2), brk(2), chmod(2), exit(2),
fcntl(2), fork(2), getpflags(2), getrlimit(2), memcntl(2),
mmap(2), nice(2), priocntl(2), profil(2), semop(2),
shmop(2), sigpending(2), sigprocmask(2), times(2), umask(2),
lockf(3C), ptrace(3C), setlocale(3C), signal(3C),
system(3C), timer_create(3RT), a.out(4), contract(4), attri-
butes(5), environ(5), privileges(5), standards(5)
WARNINGS
If a program is setuid to a user ID other than the
superuser, and the program is executed when the real user ID
is super-user, then the program has some of the powers of a
super-user as well.
SunOS 5.10 Last change: 18 Dec 2003 10
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