|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
|
|
|
EXEC(3P) POSIX Programmer's Manual EXEC(3P)
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.
environ, execl, execle, execlp, execv, execve, execvp, fexecve —
execute a file
#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[]);
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.1‐2017, 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.1‐2017 shall be inherited in the new process image from the
old process image. All other thread attributes defined in this
volume of POSIX.1‐2017 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.1‐2017 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.
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.
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.
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);
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.
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.1‐2017 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-minus>
('‐') to the actual filename, which indicates to the command
interpreter being invoked that it is a ``login shell''.
Also, note that the test and [ utilities require specific strings
for the argv[0] argument to have deterministic behavior across
all implementations.
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.1‐2017 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.1‐2017 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.1‐2017 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.1‐2017 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.1‐2017 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.1‐2017, 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 (3p) 14
Set to default.
fork (3p) 14
Inherit.
pthread_create (3p) 14
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, a function
like openat() can be used to open a file which has been found by
reading the content of a directory using readdir().
None.
alarm(3p), atexit(3p), chmod(3p), close(3p), confstr(3p),
exit(3p), fcntl(3p), fork(3p), fstatvfs(3p), getenv(3p),
getitimer(3p), getrlimit(3p), mknod(3p), mmap(3p), nice(3p),
open(3p), posix_spawn(3p), posix_trace_create(3p),
posix_trace_event(3p), posix_trace_eventid_equal(3p),
pthread_atfork(3p), pthread_sigmask(3p), putenv(3p), readdir(3p),
semop(3p), setlocale(3p), shmat(3p), sigaction(3p),
sigaltstack(3p), sigpending(3p), system(3p), times(3p),
ulimit(3p), umask(3p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, unistd.h(0p)
The Shell and Utilities volume of POSIX.1‐2017, test(1p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. 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.opengroup.org/unix/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 .
IEEE/The Open Group 2017 EXEC(3P)
Pages that refer to this page: env(1)
|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|