Provided by: manpages-posix-dev_2013a-1_all 
PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of
this interface may differ (consult the corresponding Linux manual page for details of
Linux behavior), or the interface may not be implemented on Linux.
NAME
environ, execl, execle, execlp, execv, execve, execvp, fexecve — execute a file
SYNOPSIS
#include <unistd.h>
extern char **environ;
int execl(const char *path, const char *arg0, ... /*, (char *)0 */);
int execle(const char *path, const char *arg0, ... /*,
(char *)0, char *const envp[]*/);
int execlp(const char *file, const char *arg0, ... /*, (char *)0 */);
int execv(const char *path, char *const argv[]);
int execve(const char *path, char *const argv[], char *const envp[]);
int execvp(const char *file, char *const argv[]);
int fexecve(int fd, char *const argv[], char *const envp[]);
DESCRIPTION
The exec family of functions shall replace the current process image with a new process
image. The new image shall be constructed from a regular, executable file called the new
process image file. There shall be no return from a successful exec, because the calling
process image is overlaid by the new process image.
The fexecve() function shall be equivalent to the execve() function except that the file
to be executed is determined by the file descriptor fd instead of a pathname. The file
offset of fd is ignored.
When a C-language program is executed as a result of a call to one of the exec family of
functions, it shall be entered as a C-language function call as follows:
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, which must be declared by the
user if it is to be used directly:
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.
Applications can change the entire environment in a single operation by assigning the
environ variable to point to an array of character pointers to the new environment
strings. After assigning a new value to environ, applications should not rely on the new
environment strings remaining part of the environment, as a call to getenv(), putenv(),
setenv(), unsetenv(), or any function that is dependent on an environment variable may, on
noticing that environ has changed, copy the environment strings to a new array and assign
environ to point to it.
Any application that directly modifies the pointers to which the environ variable points
has undefined behavior.
Conforming multi-threaded applications shall not use the environ variable to access or
modify any environment variable while any other thread is concurrently modifying any
environment variable. A call to any function dependent on any environment variable shall
be considered a use of the environ variable to access that environment variable.
The arguments specified by a program with one of the exec functions shall be passed on to
the new process image in the corresponding main() arguments.
The argument path points to a pathname that identifies the new process image file.
The argument file is used to construct a pathname that identifies the new process image
file. If the file argument contains a <slash> character, the file argument shall be used
as the pathname for this file. Otherwise, the path prefix for this file is obtained by a
search of the directories passed as the environment variable PATH (see the Base
Definitions volume of POSIX.1‐2008, Chapter 8, Environment Variables). If this
environment variable is not present, the results of the search are implementation-defined.
There are two distinct ways in which the contents of the process image file may cause the
execution to fail, distinguished by the setting of errno to either [ENOEXEC] or [EINVAL]
(see the ERRORS section). In the cases where the other members of the exec family of
functions would fail and set errno to [ENOEXEC], the execlp() and execvp() functions shall
execute a command interpreter and the environment of the executed command shall be as if
the process invoked the sh utility using execl() as follows:
execl(<shell path>, arg0, file, arg1, ..., (char *)0);
where <shell path> is an unspecified pathname for the sh utility, file is the process
image file, and for execvp(), where arg0, arg1, and so on correspond to the values passed
to execvp() in argv[0], argv[1], and so on.
The arguments represented by arg0,... are pointers to null-terminated character strings.
These strings shall constitute the argument list available to the new process image. The
list is terminated by a null pointer. The argument arg0 should point to a filename string
that is associated with the process being started by one of the exec functions.
The argument argv is an array of character pointers to null-terminated strings. The
application shall ensure that the last member of this array is a null pointer. These
strings shall constitute the argument list available to the new process image. The value
in argv[0] should point to a filename string that is associated with the process being
started by one of the exec functions.
The argument envp is an array of character pointers to null-terminated strings. These
strings shall constitute the environment for the new process image. The envp array is
terminated by a null pointer.
For those forms not containing an envp pointer (execl(), execv(), execlp(), and execvp()),
the environment for the new process image shall be taken from the external variable
environ in the calling process.
The number of bytes available for the new process' combined argument and environment lists
is {ARG_MAX}. It is implementation-defined whether null terminators, pointers, and/or any
alignment bytes are included in this total.
File descriptors open in the calling process image shall remain open in the new process
image, except for those whose close-on-exec flag FD_CLOEXEC is set. For those file
descriptors that remain open, all attributes of the open file description remain
unchanged. For any file descriptor that is closed for this reason, file locks are removed
as a result of the close as described in close(). Locks that are not removed by closing
of file descriptors remain unchanged.
If file descriptor 0, 1, or 2 would otherwise be closed after a successful call to one of
the exec family of functions, implementations may open an unspecified file for the file
descriptor in the new process image. If a standard utility or a conforming application is
executed with file descriptor 0 not open for reading or with file descriptor 1 or 2 not
open for writing, the environment in which the utility or application is executed shall be
deemed non-conforming, and consequently the utility or application might not behave as
described in this standard.
Directory streams open in the calling process image shall be closed in the new process
image.
The state of the floating-point environment in the initial thread of the new process image
shall be set to the default.
The state of conversion descriptors and message catalog descriptors in the new process
image is undefined.
For the new process image, the equivalent of:
setlocale(LC_ALL, "C")
shall be executed at start-up.
Signals set to the default action (SIG_DFL) in the calling process image shall be set to
the default action in the new process image. Except for SIGCHLD, signals set to be
ignored (SIG_IGN) by the calling process image shall be set to be ignored by the new
process image. Signals set to be caught by the calling process image shall be set to the
default action in the new process image (see <signal.h>).
If the SIGCHLD signal is set to be ignored by the calling process image, it is unspecified
whether the SIGCHLD signal is set to be ignored or to the default action in the new
process image.
After a successful call to any of the exec functions, alternate signal stacks are not
preserved and the SA_ONSTACK flag shall be cleared for all signals.
After a successful call to any of the exec functions, any functions previously registered
by the atexit() or pthread_atfork() functions are no longer registered.
If the ST_NOSUID bit is set for the file system containing the new process image file,
then the effective user ID, effective group ID, saved set-user-ID, and saved set-group-ID
are unchanged in the new process image. Otherwise, if the set-user-ID mode bit of the new
process image file is set, the effective user ID of the new process image shall be set to
the user 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 shall be
set to the group ID of the new process image file. The real user ID, real group ID, and
supplementary group IDs of the new process image shall remain the same as those of the
calling process image. The effective user ID and effective group ID of the new process
image shall be saved (as the saved set-user-ID and the saved set-group-ID) for use by
setuid().
Any shared memory segments attached to the calling process image shall not be attached to
the new process image.
Any named semaphores open in the calling process shall be closed as if by appropriate
calls to sem_close().
Any blocks of typed memory that were mapped in the calling process are unmapped, as if
munmap() was implicitly called to unmap them.
Memory locks established by the calling process via calls to mlockall() or mlock() shall
be removed. If locked pages in the address space of the calling process are also mapped
into the address spaces of other processes and are locked by those processes, the locks
established by the other processes shall be unaffected by the call by this process to the
exec function. If the exec function fails, the effect on memory locks is unspecified.
Memory mappings created in the process are unmapped before the address space is rebuilt
for the new process image.
When the calling process image does not use the SCHED_FIFO, SCHED_RR, or SCHED_SPORADIC
scheduling policies, the scheduling policy and parameters of the new process image and the
initial thread in that new process image are implementation-defined.
When the calling process image uses the SCHED_FIFO, SCHED_RR, or SCHED_SPORADIC scheduling
policies, the process policy and scheduling parameter settings shall not be changed by a
call to an exec function. The initial thread in the new process image shall inherit the
process scheduling policy and parameters. It shall have the default system contention
scope, but shall inherit its allocation domain from the calling process image.
Per-process timers created by the calling process shall be deleted before replacing the
current process image with the new process image.
All open message queue descriptors in the calling process shall be closed, as described in
mq_close().
Any outstanding asynchronous I/O operations may be canceled. Those asynchronous I/O
operations that are not canceled shall complete as if the exec function had not yet
occurred, but any associated signal notifications shall be suppressed. It is unspecified
whether the exec function itself blocks awaiting such I/O completion. In no event,
however, shall the new process image created by the exec function be affected by the
presence of outstanding asynchronous I/O operations at the time the exec function is
called. Whether any I/O is canceled, and which I/O may be canceled upon exec, is
implementation-defined.
The new process image shall inherit the CPU-time clock of the calling process image. This
inheritance means that the process CPU-time clock of the process being exec-ed shall not
be reinitialized or altered as a result of the exec function other than to reflect the
time spent by the process executing the exec function itself.
The initial value of the CPU-time clock of the initial thread of the new process image
shall be set to zero.
If the calling process is being traced, the new process image shall continue to be traced
into the same trace stream as the original process image, but the new process image shall
not inherit the mapping of trace event names to trace event type identifiers that was
defined by calls to the posix_trace_eventid_open() or the posix_trace_trid_eventid_open()
functions in the calling process image.
If the calling process is a trace controller process, any trace streams that were created
by the calling process shall be shut down as described in the posix_trace_shutdown()
function.
The thread ID of the initial thread in the new process image is unspecified.
The size and location of the stack on which the initial thread in the new process image
runs is unspecified.
The initial thread in the new process image shall have its cancellation type set to
PTHREAD_CANCEL_DEFERRED and its cancellation state set to PTHREAD_CANCEL_ENABLED.
The initial thread in the new process image shall have all thread-specific data values set
to NULL and all thread-specific data keys shall be removed by the call to exec without
running destructors.
The initial thread in the new process image shall be joinable, as if created with the
detachstate attribute set to PTHREAD_CREATE_JOINABLE.
The new process shall inherit at least the following attributes from the calling process
image:
* Nice value (see nice())
* semadj values (see semop())
* Process ID
* Parent process ID
* Process group ID
* Session membership
* Real user ID
* Real group ID
* Supplementary group IDs
* Time left until an alarm clock signal (see alarm())
* Current working directory
* Root directory
* File mode creation mask (see umask())
* File size limit (see getrlimit() and setrlimit())
* Process signal mask (see pthread_sigmask())
* Pending signal (see sigpending())
* tms_utime, tms_stime, tms_cutime, and tms_cstime (see times())
* Resource limits
* Controlling terminal
* Interval timers
The initial thread of the new process shall inherit at least the following attributes from
the calling thread:
* Signal mask (see sigprocmask() and pthread_sigmask())
* Pending signals (see sigpending())
All other process attributes defined in this volume of POSIX.1‐2008 shall be inherited in
the new process image from the old process image. All other thread attributes defined in
this volume of POSIX.1‐2008 shall be inherited in the initial thread in the new process
image from the calling thread in the old process image. The inheritance of process or
thread attributes not defined by this volume of POSIX.1‐2008 is implementation-defined.
A call to any exec function from a process with more than one thread shall result in all
threads being terminated and the new executable image being loaded and executed. No
destructor functions or cleanup handlers shall be called.
Upon successful completion, the exec functions shall mark for update the last data access
timestamp of the file. If an exec function failed but was able to locate the process image
file, whether the last data access timestamp is marked for update is unspecified. Should
the exec function succeed, the process image file shall be considered to have been opened
with open(). The corresponding close() shall be 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, posix_spawn(), or posix_spawnp(). The argv[] and envp[] arrays of
pointers and the strings to which those arrays point shall not be modified by a call to
one of the exec functions, except as a consequence of replacing the process image.
The saved resource limits in the new process image are set to be a copy of the process'
corresponding hard and soft limits.
RETURN VALUE
If one of the exec functions returns to the calling process image, an error has occurred;
the return value shall be −1, and errno shall be set to indicate the error.
ERRORS
The exec functions shall fail if:
E2BIG The number of bytes used by the new process image's argument list and environment
list is greater than the system-imposed limit of {ARG_MAX} bytes.
EACCES The new process image file is not a regular file and the implementation does not
support execution of files of its type.
EINVAL The new process image file has appropriate privileges and has a recognized
executable binary format, but the system does not support execution of a file with
this format.
The exec functions, except for fexecve(), shall fail if:
EACCES Search permission is denied for a directory listed in the new process image file's
path prefix, or the new process image file denies execution permission.
ELOOP A loop exists in symbolic links encountered during resolution of the path or file
argument.
ENAMETOOLONG
The length of a component of a pathname is longer than {NAME_MAX}.
ENOENT A component of path or file does not name an existing file or path or file is an
empty string.
ENOTDIR
A component of the new process image file's path prefix names an existing file that
is neither a directory nor a symbolic link to a directory, or the new process image
file's pathname contains at least one non-<slash> character and ends with one or
more trailing <slash> characters and the last pathname component names an existing
file that is neither a directory nor a symbolic link to a directory.
The exec functions, except for execlp() and execvp(), shall fail if:
ENOEXEC
The new process image file has the appropriate access permission but has an
unrecognized format.
The fexecve() function shall fail if:
EBADF The fd argument is not a valid file descriptor open for executing.
The exec functions may fail if:
ENOMEM The new process image requires more memory than is allowed by the hardware or
system-imposed memory management constraints.
The exec functions, except for fexecve(), may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the
path or file argument.
ENAMETOOLONG
The length of the path argument or the length of the pathname constructed from the
file argument exceeds {PATH_MAX}, or pathname resolution of a symbolic link
produced an intermediate result with a length that exceeds {PATH_MAX}.
ETXTBSY
The new process image file is a pure procedure (shared text) file that is currently
open for writing by some process.
The following sections are informative.
EXAMPLES
Using execl()
The following example executes the ls command, specifying the pathname of the executable
(/bin/ls) and using arguments supplied directly to the command to produce single-column
output.
#include <unistd.h>
int ret;
...
ret = execl ("/bin/ls", "ls", "-1", (char *)0);
Using execle()
The following example is similar to Using execl(). In addition, it specifies the
environment for the new process image using the env argument.
#include <unistd.h>
int ret;
char *env[] = { "HOME=/usr/home", "LOGNAME=home", (char *)0 };
...
ret = execle ("/bin/ls", "ls", "-l", (char *)0, env);
Using execlp()
The following example searches for the location of the ls command among the directories
specified by the PATH environment variable.
#include <unistd.h>
int ret;
...
ret = execlp ("ls", "ls", "-l", (char *)0);
Using execv()
The following example passes arguments to the ls command in the cmd array.
#include <unistd.h>
int ret;
char *cmd[] = { "ls", "-l", (char *)0 };
...
ret = execv ("/bin/ls", cmd);
Using execve()
The following example passes arguments to the ls command in the cmd array, and specifies
the environment for the new process image using the env argument.
#include <unistd.h>
int ret;
char *cmd[] = { "ls", "-l", (char *)0 };
char *env[] = { "HOME=/usr/home", "LOGNAME=home", (char *)0 };
...
ret = execve ("/bin/ls", cmd, env);
Using execvp()
The following example searches for the location of the ls command among the directories
specified by the PATH environment variable, and passes arguments to the ls command in the
cmd array.
#include <unistd.h>
int ret;
char *cmd[] = { "ls", "-l", (char *)0 };
...
ret = execvp ("ls", cmd);
APPLICATION USAGE
As the state of conversion descriptors and message catalog descriptors in the new process
image is undefined, conforming 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 as the global locale in the
new process image should call setlocale() with the appropriate parameters.
When assigning a new value to the environ variable, applications should ensure that the
environment to which it will point contains at least the following:
1. Any implementation-defined variables required by the implementation to provide a
conforming environment. See the _CS_V7_ENV entry in <unistd.h> and confstr() for
details.
2. A value for PATH which finds conforming versions of all standard utilities before any
other versions.
The same constraint applies to the envp array passed to execle() or execve(), in order to
ensure that the new process image is invoked in a conforming environment.
Applications should not execute programs with file descriptor 0 not open for reading or
with file descriptor 1 or 2 not open for writing, as this might cause the executed program
to misbehave. In order not to pass on these file descriptors to an executed program,
applications should not just close them but should reopen them on, for example, /dev/null.
Some implementations may reopen them automatically, but applications should not rely on
this being done.
If an application wants to perform a checksum test of the file being executed before
executing it, the file will need to be opened with read permission to perform the checksum
test.
Since execute permission is checked by fexecve(), the file description fd need not have
been opened with the O_EXEC flag. However, if the file to be executed denies read and
write permission for the process preparing to do the exec, the only way to provide the fd
to fexecve() will be to use the O_EXEC flag when opening fd. In this case, the
application will not be able to perform a checksum test since it will not be able to read
the contents of the file.
Note that when a file descriptor is opened with O_RDONLY, O_RDWR, or O_WRONLY mode, the
file descriptor can be used to read, read and write, or write the file, respectively, even
if the mode of the file changes after the file was opened. Using the O_EXEC open mode is
different; fexecve() will ignore the mode that was used when the file descriptor was
opened and the exec will fail if the mode of the file associated with fd does not grant
execute permission to the calling process at the time fexecve() is called.
RATIONALE
Early proposals required that the value of argc passed to main() be ``one or greater''.
This was driven by the same requirement in drafts of the ISO C standard. In fact,
historical implementations have passed a value of zero when no arguments are supplied to
the caller of the exec functions. This requirement was removed from the ISO C standard and
subsequently removed from this volume of POSIX.1‐2008 as well. The wording, in particular
the use of the word should, requires a Strictly Conforming POSIX Application to pass at
least one argument to the exec function, thus guaranteeing that argc be one or greater
when invoked by such an application. In fact, this is good practice, since many existing
applications reference argv[0] without first checking the value of argc.
The requirement on a Strictly Conforming POSIX Application also states that the value
passed as the first argument be a filename string associated with the process being
started. Although some existing applications pass a pathname rather than a filename string
in some circumstances, a filename string is more generally useful, since the common usage
of argv[0] is in printing diagnostics. In some cases the filename passed is not the actual
filename of the file; for example, many implementations of the login utility use a
convention of prefixing a <hyphen> ('‐') to the actual filename, which indicates to the
command interpreter being invoked that it is a ``login shell''.
Historically, there have been two ways that implementations can exec shell scripts.
One common historical implementation is that the execl(), execv(), execle(), and execve()
functions return an [ENOEXEC] error for any file not recognizable as executable, including
a shell script. When the execlp() and execvp() functions encounter such a file, they
assume the file to be a shell script and invoke a known command interpreter to interpret
such files. This is now required by POSIX.1‐2008. These implementations of execvp() and
execlp() only give the [ENOEXEC] error in the rare case of a problem with the command
interpreter's executable file. Because of these implementations, the [ENOEXEC] error is
not mentioned for execlp() or execvp(), although implementations can still give it.
Another way that some historical implementations handle shell scripts is by recognizing
the first two bytes of the file as the character string "#!" and using the remainder of
the first line of the file as the name of the command interpreter to execute.
One potential source of confusion noted by the standard developers is over how the
contents of a process image file affect the behavior of the exec family of functions. The
following is a description of the actions taken:
1. If the process image file is a valid executable (in a format that is executable and
valid and having appropriate privileges) for this system, then the system executes the
file.
2. If the process image file has appropriate privileges and is in a format that is
executable but not valid for this system (such as a recognized binary for another
architecture), then this is an error and errno is set to [EINVAL] (see later RATIONALE
on [EINVAL]).
3. If the process image file has appropriate privileges but is not otherwise recognized:
a. If this is a call to execlp() or execvp(), then they invoke a command interpreter
assuming that the process image file is a shell script.
b. If this is not a call to execlp() or execvp(), then an error occurs and errno is
set to [ENOEXEC].
Applications that do not require to access their arguments may use the form:
main(void)
as specified in the ISO C standard. However, the implementation will always provide the
two arguments argc and argv, even if they are not used.
Some implementations provide a third argument to main() called envp. This is defined as a
pointer to the environment. The ISO C standard specifies invoking main() with two
arguments, so implementations must support applications written this way. Since this
volume of POSIX.1‐2008 defines the global variable environ, which is also provided by
historical implementations and can be used anywhere that envp could be used, there is no
functional need for the envp argument. Applications should use the getenv() function
rather than accessing the environment directly via either envp or environ.
Implementations are required to support the two-argument calling sequence, but this does
not prohibit an implementation from supporting envp as an optional third argument.
This volume of POSIX.1‐2008 specifies that signals set to SIG_IGN remain set to SIG_IGN,
and that the new process image inherits the signal mask of the thread that called exec in
the old process image. This is consistent with historical implementations, and it permits
some useful functionality, such as the nohup command. However, it should be noted that
many existing applications wrongly assume that they start with certain signals set to the
default action and/or unblocked. In particular, applications written with a simpler signal
model that does not include blocking of signals, such as the one in the ISO C standard,
may not behave properly if invoked with some signals blocked. Therefore, it is best not to
block or ignore signals across execs without explicit reason to do so, and especially not
to block signals across execs of arbitrary (not closely cooperating) programs.
The exec functions always save the value of the effective user ID and effective group ID
of the process at the completion of the exec, whether or not the set-user-ID or the set-
group-ID bit of the process image file is set.
The statement about argv[] and envp[] being constants is included to make explicit to
future writers of language bindings that these objects are completely constant. Due to a
limitation of the ISO C standard, it is not possible to state that idea in standard C.
Specifying two levels of const−qualification for the argv[] and envp[] parameters for the
exec functions may seem to be the natural choice, given that these functions do not modify
either the array of pointers or the characters to which the function points, but this
would disallow existing correct code. Instead, only the array of pointers is noted as
constant. The table of assignment compatibility for dst=src derived from the ISO C
standard summarizes the compatibility:
┌────────────────────┬──────────┬────────────────┬───────────────┬─────────────────────┐
│ dst: │ char *[] │ const char *[] │ char *const[] │ const char *const[] │
├────────────────────┼──────────┼────────────────┼───────────────┼─────────────────────┤
│src: │ │ │ │ │
│char *[] │ VALID │ — │ VALID │ — │
│const char *[] │ — │ VALID │ — │ VALID │
│char * const [] │ — │ — │ VALID │ — │
│const char *const[] │ — │ — │ — │ VALID │
└────────────────────┴──────────┴────────────────┴───────────────┴─────────────────────┘
Since all existing code has a source type matching the first row, the column that gives
the most valid combinations is the third column. The only other possibility is the fourth
column, but using it would require a cast on the argv or envp arguments. It is unfortunate
that the fourth column cannot be used, because the declaration a non-expert would
naturally use would be that in the second row.
The ISO C standard and this volume of POSIX.1‐2008 do not conflict on the use of environ,
but some historical implementations of environ may cause a conflict. As long as environ is
treated in the same way as an entry point (for example, fork()), it conforms to both
standards. A library can contain fork(), but if there is a user-provided fork(), that
fork() is given precedence and no problem ensues. The situation is similar for environ:
the definition in this volume of POSIX.1‐2008 is to be used if there is no user-provided
environ to take precedence. At least three implementations are known to exist that solve
this problem.
E2BIG The limit {ARG_MAX} applies not just to the size of the argument list, but to the
sum of that and the size of the environment list.
EFAULT Some historical systems return [EFAULT] rather than [ENOEXEC] when the new process
image file is corrupted. They are non-conforming.
EINVAL This error condition was added to POSIX.1‐2008 to allow an implementation to detect
executable files generated for different architectures, and indicate this situation
to the application. Historical implementations of shells, execvp(), and execlp()
that encounter an [ENOEXEC] error will execute a shell on the assumption that the
file is a shell script. This will not produce the desired effect when the file is a
valid executable for a different architecture. An implementation may now choose to
avoid this problem by returning [EINVAL] when a valid executable for a different
architecture is encountered. Some historical implementations return [EINVAL] to
indicate that the path argument contains a character with the high order bit set.
The standard developers chose to deviate from historical practice for the following
reasons:
1. The new utilization of [EINVAL] will provide some measure of utility to
the user community.
2. Historical use of [EINVAL] is not acceptable in an internationalized
operating environment.
ENAMETOOLONG
Since the file pathname may be constructed by taking elements in the PATH variable
and putting them together with the filename, the [ENAMETOOLONG] error condition
could also be reached this way.
ETXTBSY
System V returns this error when the executable file is currently open for writing
by some process. This volume of POSIX.1‐2008 neither requires nor prohibits this
behavior.
Other systems (such as System V) may return [EINTR] from exec. This is not addressed by
this volume of POSIX.1‐2008, but implementations may have a window between the call to
exec and the time that a signal could cause one of the exec calls to return with [EINTR].
An explicit statement regarding the floating-point environment (as defined in the <fenv.h>
header) was added to make it clear that the floating-point environment is set to its
default when a call to one of the exec functions succeeds. The requirements for
inheritance or setting to the default for other process and thread start-up functions is
covered by more generic statements in their descriptions and can be summarized as follows:
posix_spawn() Set to default.
fork() Inherit.
pthread_create()
Inherit.
The purpose of the fexecve() function is to enable executing a file which has been
verified to be the intended file. It is possible to actively check the file by reading
from the file descriptor and be sure that the file is not exchanged for another between
the reading and the execution. Alternatively, an function like openat() can be used to
open a file which has been found by reading the content of a directory using readdir().
FUTURE DIRECTIONS
None.
SEE ALSO
alarm(), atexit(), chmod(), close(), confstr(), exit(), fcntl(), fork(), fstatvfs(),
getenv(), getitimer(), getrlimit(), mknod(), mmap(), nice(), open(), posix_spawn(),
posix_trace_create(), posix_trace_event(), posix_trace_eventid_equal(), pthread_atfork(),
pthread_sigmask(), putenv(), readdir(), semop(), setlocale(), shmat(), sigaction(),
sigaltstack(), sigpending(), system(), times(), ulimit(), umask()
The Base Definitions volume of POSIX.1‐2008, Chapter 8, Environment Variables, <unistd.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any
discrepancy between this version and the original IEEE and The Open Group Standard, the
original IEEE and The Open Group Standard is the referee document. The original Standard
can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are most likely to have
been introduced during the conversion of the source files to man page format. To report
such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .