System Calls exec(2)
NAME
exec, execl, execle, execlp, execv, execve, execvp - execute
a fileSYNOPSIS
#include
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 calledthe new process image file. This file is either an execut-
able object file or a file of data for an interpreter. Thereis 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 remainingSunOS 5.11 Last change: 16 Jun 2008 1
System Calls exec(2) arguments to the interpreter are arg0 through argn of the originally 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: int main (int argc, char *argv[]); where argc is the argument count and argv is an array of character pointers to the arguments themselves. In addition, the following variable: extern char **environ; is initialized as a pointer to 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 obtainedby 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 theSunOS 5.11 Last change: 16 Jun 2008 2
System Calls exec(2) 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 tonull-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 tonull-terminated strings. These strings constitute the
environment for the new process image. The envp array is 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 combinedargument 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 whoseclose-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.SunOS 5.11 Last change: 16 Jun 2008 3
System Calls exec(2) 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 stacksare 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 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 processimage are saved (as the saved set-user-ID and the saved
set-group-ID for use by setuid(2).
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System Calls exec(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 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 closedas if by appropriate calls to sem_close(3C)
Profiling is disabled for the new process; see profil(2).Timers created by the calling process with timer_create(3C)
are deleted before replacing the current process image withSunOS 5.11 Last change: 16 Jun 2008 5
System Calls exec(2) 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 processare closed, as described in mq_close(3C).
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 functionitself 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 controlling terminal o current working directory
o file-locks (see fcntl(2) and lockf(3C))
o file mode creation mask (see umask(2)) o file size limit (see ulimit(2)) o limit privilege set o nice value (see nice(2)) o parent process ID o pending signals (see sigpending(2)) o privilege debugging flag (see privileges(5) and getpflags(2)) o process IDSunOS 5.11 Last change: 16 Jun 2008 6
System Calls exec(2) o process contract (see contract(4) and process(4)) o process group ID o process signal mask (see sigprocmask(2))o processor bindings (see processor_bind(2))
o processor set bindings (see pset_bind(2))
o project ID o real group ID o real user ID o resource limits (see getrlimit(2)) o root directory o scheduler class and priority (see priocntl(2)) o semadj values (see semop(2)) o session membership (see exit(2) and signal(3C)) o supplementary group IDs o task ID o time left until an alarm clock signal (see alarm(2))o tms_utime, tms_stime, tms_cutime, and tms_cstime
(see times(2)) o trace flag (see ptrace(3C) request 0) A call to any exec function from a process with more than one thread results in all threads being terminated and thenew executable image being loaded and executed. No destruc-
tor functions will be called. Upon successful completion, each of the functions in theexec family marks for update the st_atime field of the file.
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 occurSunOS 5.11 Last change: 16 Jun 2008 7
System Calls exec(2) 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 modifiedby 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'sargument 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 directorylisted 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. EAGAIN Total amount of system memory available whenreading using raw I/O is temporarily insuf-
ficient. EFAULT An argument points to an illegal address.SunOS 5.11 Last change: 16 Jun 2008 8
System Calls exec(2)EINVAL The new process image file has the appropri-
ate permission and has a recognized execut-
able binary format, but the system does notsupport 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. The exec functions, except for execlp() and execvp(), will fail if: ENOEXEC The new process image file has the appropriateaccess permission but is not in the proper for-
mat. The exec functions may fail if:ENAMETOOLONG Pathname resolution of a symbolic link pro-
duced an intermediate result whose lengthexceeds {PATH_MAX}.
SunOS 5.11 Last change: 16 Jun 2008 9
System Calls exec(2) ENOMEM The new process image requires more memorythan 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 POSIXlocale 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:____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
|_____________________________|_____________________________|
| Interface Stability | Committed ||_____________________________|_____________________________|
| MT-Level | See below. |
|_____________________________|_____________________________|
| Standard | See standards(5). ||_____________________________|_____________________________|
The execle() and execve() functions 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),SunOS 5.11 Last change: 16 Jun 2008 10
System Calls exec(2)system(3C), timer_create(3C), a.out(4), contract(4), pro-
cess(4), attributes(5), environ(5), privileges(5), stan-
dards(5) WARNINGS If a program is setuid to a user ID other than the superuser, and the program is executed when the real user IDis super-user, then the program has some of the powers of a
super-user as well.
SunOS 5.11 Last change: 16 Jun 2008 11