程序执行函数

注释

Warning

以加锁方式打开的文件（特别是在打开会话时）， 必须在执行后台程序之前关闭。

参见

这些函数和 执行运算符 是紧密关联的。 因此，当运行在 安全模式 是，你必须考虑 safe_mode_exec_dir 指示。

Table of Contents

  • escapeshellarg — 把字符串转码为可以在 shell 命令里使用的参数
  • escapeshellcmd — shell 元字符转义
  • exec — 执行一个外部程序
  • passthru — 执行外部程序并且显示原始输出
  • proc_close — 关闭由 proc_open 打开的进程并且返回进程退出码
  • proc_get_status — 获取由 proc_open 函数打开的进程的信息
  • proc_nice — 修改当前进程的优先级
  • proc_open — 执行一个命令，并且打开用来输入/输出的文件指针。
  • proc_terminate — 杀除由 proc_open 打开的进程
  • shell_exec — 通过 shell 环境执行命令，并且将完整的输出以字符串的方式返回。
  • system — 执行外部程序，并且显示输出

User Contributed Notes

HappyDog, kennel17.co.uk 04-Mar-2017 09:35
Just following up my previous post, in reply to lancelot--du-lac at hotmail dot fr:

The behaviour described was fixed in PHP 5.3 in the following commit:

https://github.com/php/php-src/commit/19322fc782af429938da8d3b421c0807cf1b848a#diff-15f2d3ef68f383a87cce668765721041R221

To replicate the fix in your own code, so it also runs on PHP 5.2, instead of:

<?php
$cmd = "...any shell command, maybe with multiple quotes...";
exec($cmd);
?>

use

<?php
$cmd = "...any shell command, maybe with multiple quotes...";

if (strtoupper(substr(php_uname('s'), 0, 3)) == "WIN"
    && version_compare(PHP_VERSION, "5.3", "<"))
{
    $cmd = '"' . $cmd . '"';
}

exec($cmd);
?>

This replicates the behaviour of PHP 5.3 and above.  Note that this applies to all shell commands (not just exec(), as used in my example).
HappyDog, kennel17.co.uk 04-Mar-2017 08:22
In response to lancelot--du-lac at hotmail dot fr, who pointed out some issues with commands containing multiple quoted strings when calling shell functions on Windows:  I have also recently encountered this issue when trying to run my code on PHP 5.2.  The code runs fine on PHP 5.3 and above so I guess the problem has been fixed (though I couldn't find a mention of it in the PHP release notes), but on 5.2 it behaves as described in that post.

Although the original post says there was no output, this isn't quite right.  The reason there was no output is because the error is being sent to stderr, which wasn't being captured.  Adding " 2>&1" to the end of the command means you also see this output.  This ends up being quite illuminating; I was getting was something like this:

  'C:\Program' is not recognized as an internal or external command,
  operable program or batch file.

Clearly, having two quoted strings in the command confuses the shell commands; the result is the same as if you ran the command without any quotes.

I haven't found a workaround for anyone who still needs to support 5.2, but as I say, it doesn't seem to be an issue on later PHP versions.

[Note: I was also testing on Windows XP (SP3), so I am not sure if this was a general Windows issue or specific to XP.]
benkitzelman at yahoo dot co dot uk 20-Aug-2010 05:02
Within Linux, when calling the php interpreter directly from popen, or other program execution function to execute a script, it appears as though the script perpetually fails and re-executes.

i.e. <?php popen("php myscript.php&", "w"); // fail ?>

As each re-execution causes the executing script to load under a new PID, it is incredibly difficult to identify and kill the process manually.

[One solution is] to ensure the executing script has a valid shebang, and execute permissions. This allows you to execute the script directly

i.e. <?php popen("./myscript.php", "w"); // ok ?>
Anonymous 09-Jul-2008 07:34
I found this comment on this page:

[begin of quote]
Trying to us the following code failed badly with various results: like "unable to fork", "access denied", "empty results", depending on what settings I used, ... even though the same code worked from command line on the server itself.

$retstr = exec('nslookup -type=mx myhost.com', $retarr);

Instead of nslookup I believe this would apply to most programs from the \system32\ directory.

I had to learn that the following finally worked:
$retstr = exec('c:\php\safedir\nslookup -type=mx myhost.com', $retarr);

... but only under the listed preconditions:
1: nslookup.exe is placed (copied) in the directory \php\safedir\
2: the directory \php\safedir\ is included in the system PATH environement variable
3: the file cmd.exe is placed in \php\ as listed by other notes above
4: the directory "c:\php\safedir\" is set in the php.ini setting
safe_mode_exec_dir = "c:\php\safedir\"
.. maybe set in php-activescript.ini as well, depending on your system setup.
5: nslookup is referenced by the full path as otherwise the file from \windows\system32\ will be called. This happend to me with empty result due to missing rights!

Hope this helps somebody saving some time and headaches.
[end of quote]

This is just to complicated. Only two things are needed:
1. Specific permissions for the IUSR account for read & execute to the cmd.exe in C:\Windows\System32 directory
2. Specific permissions for the IUSR account for read & execute to the command that's needed (example: nslookup.exe in C:\Widnows\System23 directory)

With just this two conditions the exec works fine

(This is for an IIS server running on a windows platform)
mosesdinakaran at yahoo dot co dot in 17-Mar-2008 03:49
Hi

     I had  problem with executing   exec(),shell_exec() (PHP is not running on Safe Mode).

     After spending some time I was able to find out that the Problem is  with SELinux enabled in my system.

      You can make sure about this by seeing the log  /var/log/messages
     So I disabled SELinux and now everything works.

     A Temporary  Disable to selinux #> setenforce 0;

     Since I felt this is not a good Idea I still went through some sites and find a solution which I felt good.

     Fedora's SELinux policy has some booleans - let's see what it has for our apache:
# /usr/sbin/getsebool -a | grep httpd
allow_httpd_anon_write -- off
allow_httpd_mod_auth_pam -- off
allow_httpd_sys_script_anon_write -- off
httpd_builtin_scripting -- on
httpd_can_network_connect -- off
httpd_can_network_connect_db -- off
httpd_can_network_relay -- off
httpd_disable_trans -- off
httpd_enable_cgi -- on
httpd_enable_ftp_server -- off
httpd_enable_homedirs -- on
httpd_rotatelogs_disable_trans -- off
httpd_ssi_exec --off
httpd_suexec_disable_trans -- off
httpd_tty_comm -- off
httpd_unified -- on
 
   From the above we can make sure that exec() is not working  because of this httpd_ssi_exec -- off   setting
  So I turned it On.
  
#> setsebool -P httpd_ssi_exec 1;
 
    Now I was able to see the output of shell_exec('ls -al')

Moses
luko post cz 30-Jan-2008 03:15
to lancelot:

it's simple exec($my_cmd) on windows executes 'cmd /c $my_cmd'
if there are any spaces in $my_cmd you have to put it in doublequotes:
cmd /c "$app $target" will work

further if there are any spaces in $app and $target they also have to be in doublequotes:
cmd /c ""$app" "$target""

therefore enclose your $cmd in two more doublequotes and dont forget to escape slashes \\

$cmd = "\"\"C:\\my path with spaces\\targetapp.exe\" \"C:\\mypathnospaces\\targetfile.xxx\"\"";

and exec($cmd) will work :)
no chdir anymore...
lancelot--du-lac at hotmail dot fr 25-Jan-2008 08:00
The note is about usage of exec() under windows...

In replay to k dot mitz dot NO_SPAM at att dot NO_SPAM dot net: why not enclose your $cmd in simple quotes instead?

Here is where i'm at right now (also TRYING to use exec() and passthru() on windows XP sp2):

you can do this:

$cmd = '"C:\my path with spaces\targetapp.exe" C:\mypathnospaces\targetfile.xxx';
exec($cmd);

The above works.
________

Or, you can put your script into your directory C:\my path with spaces\, and work with php directly from there:

$cmd = 'targetapp.exe "C:\my other path with spaces\targetfile.xxx"';
exec($cmd);

The above also works, provided of course your script has the correct working directory.
________

But... In your cmd.exe, you can issue:

"C:\my path with spaces\targetapp.exe" "C:\my other path with spaces\targetfile.xxx"

Although the above works perfectly in the cmd, the following php script does NOT work on my system:

$cmd = '"C:\my path with spaces\targetapp.exe" "C:\my other path with spaces\targetfile.xxx"';
exec($cmd,&$content);

Not that it sends an error, it just does nothing, and you get nothing written into your $content array... Not that I do understand why.
________

As far as my few tryings go, the root of the problem lies in the fact that the command to execute has two passages enclosed inside double quotes. Another command which I've had working in the cmd but NOT with php is:

'"C:\my path with spaces\Apache2\bin\Apache.exe" -w -n "Apache2" -k restart'

Maybe someone has a solution; I don't (other than using chdir).
jakster at gmx dot net 05-Jan-2008 01:56
To fork a process I use the following code

<?php

fclose(STDOUT);   //Close all output or it WON'T work
fclose(STDIN);
fclose(STDERR);

if(pcntl_fork()) {
    exit;            //Return to the caller
}

//Code to run in the background

pcntl_exec("/usr/bin/php",Array($_SERVER['argv'][1]));

?>

I call this script from my website with
<?php
function fork($script){        //run a forked php script relative to the document root. NO OUTPUT IS DISPLAYED!
    global $config;
    $cmd = "/usr/bin/php \"" . dirname($_SERVER['SCRIPT_FILENAME']) . "/includes/forked/forkHelper.php\" \"" . $script . "\"";
    exec($cmd);
}
?>
Odie 14-Dec-2007 09:22
When I switched our server over from running cgi mode to FastCGI I found that my exec function was no longer working in one area. I found that even when IUSR_X had read access to the appropriate areas, it could not execute the file.

Permissions on files don't seem to matter with FastCGI. You have to move any executables and files that they access outside of wwwroot. My problem was that I was running an executable that was reading a file in my web directory.
Max_R 26-Sep-2007 04:21
Just a small notice, when running PHP under MS Windows
some external command-line utilities (like 'ffmpeg.exe') output all info to stderr instead of stdout. In my case it caused apache error.log overfilling with lots of unsolicited records.
It has just taken some time for me to make the utility silent:
Simply add
">NUL 2>&1"
to the very end of your command line. It makes cmd.exe to redirect stderr to stdout and then, in one's turn, redirect stdout to NULL.

Hope this tip will save some time when dealing with such utilities.
steve dot robinson at frogneck dot com 21-May-2007 04:46
If you are trying to use exec to run a cgi and output the contents via a php file, headers need to be seperated from the content and output seperately.

Also, at least in the case of the cgi I was attempting to execute, line feeds were missing, and some javascript didn't work as a result, so you may have to add line feeds back into the resulting output.  Here is the code I used to output my cgi properly...

<?PHP
putenv('REQUEST_METHOD=GET');

// to get your parameters passed into the cgi..
putenv('QUERY_STRING=' . $_SERVER['QUERY_STRING']);

//you will know you are past the header when you
//hit a blank line ('')
$inheader=true;
foreach($output as $val){
        if($val=='')
                $inheader=false; 
        if($inheader)
                header($val);
        else
                echo($val . "\n"); // output contents
}
?>
php at fendy dot org 03-May-2007 02:51
Scheduling WinXP tasks with schtasks.exe and using PHP to execute the command, may sometime fail to work.

This is because, Apache does not have the privilege to access some of the System Files when placing the scheduling. The way I'd do: is by creating a normal user account and assign Apache service to logon as that account.

Open the 'services.msc' in the 'Run' window, look for Apache in the listing, right click and get to 'Properties'. Click at the second tab 'Log On' and fill in the 'This account' fields.

Of course, Apache needs to be installed as Service during its first setup.

Hope this helps anyone.

Fendy Ahmad
pawel_do_not at spam_me_lenart dot pl 24-Apr-2007 01:51
You must remember that if you're running your own compiled C programs and you don't get any output you probably do it like this:

printf("some text");

shell_exec and similiar functions won't display it, you must do your output as follows:

fprintf(stdout, "some text");

and then shell_exec and so will correctly read stdout (spent an hour wondering why my program isn't working when connected with PHP :)
29-Jan-2007 05:16
it seams to me the best way would be to copy cmd.exe to a secure directory somewhere under your web directory, add it to the windows path and then call it from there using system commands. It seams as though that would get arround any security holes
Rafael Palacios 29-Jan-2007 03:52
Here is a way to collect all the output of a command (standard output and standard error):

$command="your command goes here";
$output=shell_exec($command." 2>&1");  //system call
print "<pre>$output</pre>\n";          //show output
Matt-kun 08-Dec-2006 07:50
Just a simple note to help people get rid of some headaches.

when using:
<?
       $filepath = "the path of the file";
       exec("program -command $filepath ");
       fopen($filepath,rw);
?>

Make sure you use  "\ " ( \ space) for the Linux\unix path and just " " space for fopen. These are both very basic things that you wouldn't normally think to cause a problem, but when you try to pass slashes to fopen it either breaks or even better works incorrectly =D. And vise versa for any programs that use "\ " for spaces in file paths/names.

I ran into this problem when using <? exec(" cp $path "); ?> and <? fopen("$path"); ?>. To fix it I used str_replace(" ","\ ",$path); and str_replace("\ ", " ",$path);

*Note this is alot of sudo code, and there are faster more effecient ways of doing the same operations, but I thought this might help those who were going crazy over filepaths =D.
PHP at jyoppDot-com 04-Oct-2006 07:38
Here's a function to launch a low-priority background process very simply, returning control to the foreground.  I found that a lot of the other approaches shown here allow the script to continue running, and the page is served up to the user, but the PHP thread that launched the process cannot be re-used until the process has completed.  Stdout and stderr need to be redirected to /dev/null to prevent this.

This is for BSD/*NIX servers only (tested on Fedora Core and OSX).  Win32 approaches would be necessarily very different.  Omit 'nice' if you don't want to run the process with lowered priority.

<?php
function fork($shellCmd) {
    exec("nice $shellCmd > /dev/null 2>&1 &");
}
?>
t dot kramer at NOSPAM dot safetbus dot de 21-Sep-2006 11:21
Trying to us the following code failed badly with various results: like "unable to fork", "access denied", "empty results", depending on what settings I used, ... even though the same code worked from command line on the server itself.

$retstr = exec('nslookup -type=mx myhost.com', $retarr);

Instead of nslookup I believe this would apply to most programs from the \system32\ directory.

I had to learn that the following finally worked:
$retstr = exec('c:\php\safedir\nslookup -type=mx myhost.com', $retarr);

... but only under the listed preconditions:
1: nslookup.exe is placed (copied) in the directory \php\safedir\
2: the directory \php\safedir\ is included in the system PATH environement variable
3: the file cmd.exe is placed in \php\ as listed by other notes above
4: the directory "c:\php\safedir\" is set in the php.ini setting
safe_mode_exec_dir = "c:\php\safedir\"
.. maybe set in php-activescript.ini as well, depending on your system setup.
5: nslookup is referenced by the full path as otherwise the file from \windows\system32\ will be called. This happend to me with empty result due to missing rights!

Hope this helps somebody saving some time and headaches.
Thomas
Arjan van Bentem 12-Jul-2006 09:38
When using Red Hat Fedora, beware of Security Enhanced Linux, SELinux.

Quoted from Red Hat: "The security goal is to make sure that Apache HTTP is only reading the static Web content, and not doing anything else such as writing to the content, connecting to database sockets, reading user home directories, etc."

These limitations include, among many other things, using exec to run external applications that happen to use sockets (or maybe access some files) such as HylaFAX "faxstat" as invoked from nweb2fax recvq.php and sendq.php.

For debugging, one could try running such commands using PHP Shell (see http://mgeisler.net/php-shell/) which might fail while execution from the real command line (as Unix user apache or httpd) yields no problem whatsoever.

See /var/log/messages for any denials due to the SELinux policy. To disable it:

- System, Administration, Security Level and Firewall
- open the SELinux tab
- click the Transition tree
- check Disable SELinux protection for Apache HTTP
- execute /etc/init.d/httpd restart

See also http://fedora.redhat.com/docs/selinux-faq/ and http://php.net/results.php?q=selinux&p=wholesite
judas dot iscariote at gmail dot com 01-Jun-2006 09:19
This functions are generally considered harmful,without proper input validation procedures are as worse as eval().

If what you are trying to do is possible using other mechanism, ** do it that way, even if it takes more time **.

Do not cry or blame PHP if your server gets "owned" due to a missing escapeshell*** in your code , you have been warned.
manokan at manokan dot net 18-Apr-2006 07:09
Lets make it even clearer, about the "unable to fork" error in exec().

By default Windows XP sets all permissions for cmd.exe for the temporary internet user account (IUSER-[computername]) to DENY. That overrides everthing.

You must modify the security on cmd.exe to give the IUSER-computername account at least read & execute and remove the DENY.
not at any dot com 23-Feb-2006 09:16
at LAST!  tenacity pays off, days trying every little thing!

I didn't want batch files.  I'm trying to use PHP to get rid of batch files.

I didn't want to call a file to parse the parameters to call a shell to call a file.  I've got "systems" right now with batches tiered three and five deep.

I just wanted to run stuff.

CALL, tested on WinXP, will be testing on more OSes right away, in PHP4 and 5, with exec, system, works with popen, and passthru.

here is my lame sample function.

//  CreateZip
    function createzip ($target, $archive)
    {   $ziputil = "call \"c:\\Program Files\\7-zip\\7z.exe\"";
        $archived = escapeshellarg($archive);
        $targeted = escapeshellarg($target);

        $shellcommand= $ziputil." a -tzip ".$archived." ".$targeted."\n";

  // all of the below are working in Win XP Pro
    passthru ($shellcommand);
    exec ($shellcommand);
    system ($shellcommand);
    shell_exec ($shellcommand);
    $proc= popen ($shellcommand, "r"); //$proc contains output

LONG PATH NAMES WITH SPACES IN THEM ON WINDOWS!

all in a big long concatenated command line with multiple quoted-filename parameters

shell scripting bliss!
dragomirov at tiscali dot it 24-Jan-2006 12:52
IT's great Anthony, your function works even under a *nix machine. You only need to modify like that
<?php
function callTool ($path,$file)
{
   chdir($path); $call = $path.$file;
   pclose(popen($call.' &', 'r'));
}
?>
The command goes in bakground and the script is still running.

Thanx a lot!
valqk at lozenetz dot org 25-Nov-2005 01:05
If you are chrooting php into enviornment that doesn't have /bin/sh you can't execute any command! Even when you call
mail() and it calls sendmail ... well actually sendmail NEVER gets called because /bin/sh is not in the chroot!
SO in conclusion: YOU MUST HAVE /bin/sh TO EXECUTE SOMETHING!!!
VERY IMPORTNAT!
I've lost few days while find this, hope it helps someone!!!
manokan at manokan dot net 28-Oct-2005 12:01
Even more on the "unable to fork" error.

It was driving me crazy! I did check that the permissions were set for the IUSR_[server] account to read & exec cmd.exe. Yet still it failed. It wasn't until I got desperate that I happened to look in "special permissions." (Click the advanced tab underneath the regular list of permissions.) There I found that  somehow the IUSR_[server] account had a special permission DENYING access! Of course deny overrides everything else.

This was a newly set up install of XP pro. It must be the default of something (I'd guess IIS) to set this deny permission just to make our lives miserable.
abhilashp at clariontechnologies dot co dot in 29-Sep-2005 06:58
I faced the problem of putting a shell script as a backgroud process using both exec() and system() commands on a FreeBSD Server with PHP 4.4.0

I tried all the above mentioned methods but couldnt succeded, then i coded this script and am sure will work on all Linux flavors... See if ot helps you all guys...

I Put my Shell Script in the variable $ExecCommand

and used the proc_close and proc_open functions the code is as follows :

proc_close (proc_open ($ExecCommand,array(),$somefun));

After the above line the rest of the usual  php script continues....

Hope it helps you guys..
Shaun 26-Jan-2005 10:53
Trying to use 'exec' to run a helper executable on Win2K3 (and I'm told this also happens on Win2K) from a PHP script running on IIS, failed to invoke the executable.

Running the same PHP script on Win2K using Apache to serve the page calling the same helper executable worked.

Solution: On Win2K3 (and probably Win2K), give the IIS IUSR_xxxxx guest user Read & Execute permissions to Cmd.exe found in the System32 folder under Windows root directory.

This one had me confused longer than it should have! Hope this saves others from the same fate!
louis dot j dot scoras at gmail dot com 23-Jan-2005 07:43
To start a process to run in the background, you can use the same technique you would in writing a daemon.  Fork a new child while exiting in the parent, then set that as the process leader.  Finally, fork once more, and run whatever the command is:

<?php

if(pcntl_fork()) {
    exit;
}
posix_setsid();
if(pcntl_fork()) {
    exit;
}
pcntl_exec('/usr/bin/ogg123', array('-q', $this->findPath()));

?>

Of course, this would be the last thing that your script does, because the parent exits when you spawn the new process.  You could do more fancy things, but this works as a good starting point.
margus at kohv dot com 18-Jan-2005 12:10
Well, I had this issue when I wanted to start an indefinitely running PERL script from PHP. Somehow I could not make the PHP script to return after executing the PERL script. So finally I came to following solution:

PHP file
-------------------
<?php
exec("perl /home/chatserver.pl > /dev/null");
?>
-------------------
This script will be run over HTTP.

PERL file
-------------------
#!/usr/bin/perl
fork and exit 1;

# normal code here...
-------------------

Hopefully it helps someone :)
Margus
sean @T keenio - dot - com 09-Jan-2005 08:35
Just to clarify, background shell exec()ing is not the same as a fork() under Unix. It would be useful if PHP supported fork() like Perl and other scripting languages do. Simply exec()'ing a process and sending it to the background is not the same.

A true fork() copies the current environment and duplicates the running script so that there are two instances, one child, one parent. The child and parent can determine which copy they are and then take separate courses of execution paths based on that. Often one copy will perform some "busy work" while the other returns to normal execution. But no matter what, both functions live within the same code rather than a separate, external program. exec()ing can not do this for you.
sam at freepeers dot com 02-Oct-2004 02:51
To clarify even more about what has been said in the last few posts:

"exec", "backticks", "system" and so on will fail on Windows 2003 by default. 

You must modify the security on cmd.exe to give the user account IUSR-computername the necessary permissions which are at least read & execute.
leaetherstrip at inbox dot ru 08-Jul-2004 11:23
Note on XP users: XP-Home edition does not allow to set rights directly on files and folders. You should use cacls command-line utility to do this.

For example:

cacls c:\windows\system32\cmd.exe /E /G IUSR_ADMIN2003:F

gives IIS user full access to cmd.exe (potential security hole!), so PHP can fork and execute external programs.
dotpointer 15-May-2004 03:02
Win32 / PHP 4.3.6...

If you plan to start programs on the server that show message boxes (things that require OK from the server-side), or remain (like notepad.exe), and the exec-command seems to go into an deadly loop, then MAYBE your program has started, but you can't see it. Because the web server runs as an system process, and it isn't allowed to interact with the desktop.

To solve a part of the problem (to see the programs you execute), in the control panel in Windows, goto Administration->Services, right-click the server-service, goto Properties and on the second tab (login?) and check the box about allowing the service to interact with the desktop. Click OK. Restart the webserver, and MAKE SURE it is restarted for real (i.e. look in the task manager so the service goes _down_), otherwise the desktop-option won't take.

Next phase would be to stop PHP from waiting for the processes to complete (this is what makes PHP "loop"). I solved this by creating a small Delphi-application that took the path to the file I wanted to execute and executed it by the WinExec API, which just starts the childprogram but doesn't wait for it to complete = the program completes and the PHP.exe completes the script. Problem solved!

Delphi-snippet:
WinExec(PChar(<CMD>),SW_SHOW); // replace <CMD> with the program path.
vosechu at roman-fleuve dot com 26-Mar-2004 03:35
Quick chart that helped me immensely (Best (+) / worst (o) of each command) and when to use each (w).

| exec(string cmd, [array cmd_output, [int cmd_exit_status]])
+- Second (optional) argument holds an array containing the output line by line.
+- Third (optional) argument holds the exit status of the executed program.
w- When the output of a command is only important to the program.

| system(string cmd, [int cmd_exit_status])
+- Echos ascii output straight to browser (only stdout; stderr must be redirected by putting 2>&1 after the command to see errors).
+- Second (optional) argument holds the exit status of the executed program.
w- When the output of a command is important to the user.

The more I go over my notes the less I care for the last two functions.
Shell_exec() = exec() + implode() - exit codes.
And while neccessary to be able to pipe binary through php, most people will never use passthru

| passthru(string cmd, [int cmd_exit_status])
+- Echos binary output directly to browser window.
+- Second (optional) argument holds the exit status of the executed program.
w- When the output of a command is binary.

| shell_exec(string cmd) <-- minimal features to maintain sync with normal use of backticks.
+- Returns full output as a string instead of directly to the browser (only stdout; stderr must be redirected).
o- No way to check exit status (Should use system() with both stderr and stdout redirected to /dev/null to get the exit code).
ferchland at computer-kontor dot de 22-Jan-2004 05:24
I tried to fork a GUI-process on WinNT, Apache 2, PHP4.
I saw the new process (notepad.exe) in the Task-Managers process-list, but no Notepad-Window anywhere!
After activating the checkbox "Interactive with Desktop allowed" in Services->Apache everthing works with a simple command
exec("start c:\\winnt\\notepad.exe");
jeremy at ntb dot co dot nz 28-Sep-2003 06:18
If an error occurs in the code you're trying to exec(), it can be challenging to figure out what's going wrong, since php echoes back the stdout stream rather than the stderr stream where all the useful error reporting's done. The solution is to add the code "2>&1" to the end of your shell command, which redirects stderr to stdout, which you can then easily print using something like print `shellcommand 2>&1`.
dens at dodgeball dot com 19-Sep-2003 12:41
I was stuck for about an hour and a half last night trying to get Perl to pass back values to my PHP script after running an exec() command.

Since my Perl script was using STDOUT (after being passed command lines variables), I expected the variables used in my .pl script to be accessible in PHP, no questions asked.

Of course, this wasn't working and I finally figured it out with the help of a friend (Shawn = superstar):  you need to echo the exec() command in order to get the values back into PHP. 

Since I was returning multiple values, I added pipe delimiters in my .pl script and then used PHP to parse the string to retreive my data into different variables.

Check it out:

#hit the .pl script with the data
$mydata = exec("script.pl 'command line args' ");
exec("exit(0)");
   
#parse the value that comes back from the .pl script
list($strA, $strB) = split ('[|]', $mydata);
echo "valueA: " . $strA."<br>";
echo "valueB: " . $strB."<br>";

Woo-hoo!
/d
software at yvanrodrigues dot com 29-Jul-2003 11:55
MORE ON THE UNABLE TO FORK MESSAGES IN WINDOWS:

I would like to confirm that this issue relates to permissions on %SYSTEMROOT%\SYSTEM32. The user (usually the anonymous login) must have execute permissions on cmd.exe

This is unlike most other programming languages. For example, in C the spawn and exec functions do not try to open a shell, they create the new process directly. PHP creates the new process via cmd.exe (or command.com) much like the C system() function. This is good for those of you who are trying to run batch files but this is very ineffecient for running other .exe files.

I feel uneasy about lifting permissions in my system32 directory but you can get around this by copying cmd.exe to your PHP directory. Windows will look there first and if it is not there it will check the path. Note: I mean the directory where php.exe is, not your script directory.

I have confirmed this by running filemon.exe while trying to execute a script, and you can see it trying to start the cmd.exe process.
kristof_jebens at hotmail dot com 23-Jun-2003 11:23
For WIN2K Server users running Apache 1.3.22 who are unable to run an executable...

exec('c:\\WINNT\\system32\\cmd.exe /c START c:\\file.exe');

this is the only way it worked for me.
Hope that helps
david at mego dot com dot tw 02-Jun-2003 08:48
Okay here is my two cents for Windows users having "Unable to fork..." errors when executing "shell_exec" or "system" functions.

After numerous hours of testing, I realized that this error is a result of insufficient file permissions.  You will need to locate c:\Windows\system32\cmd.exe and set the permission to at least Read & Executable for Internet Guest user accounts.

Then you should be able to run your script without a problem.  If you still have a problem feel free to contact me by email.
leenoble at spammenot dot ntlworld dot com 09-May-2003 06:37
Even I typed in the full path to a command none of the shell functions worked at all.

exec("/usr/bin/mygoodcommand");

...just didn't produce results.

The command was world executable and ran fine from the shell. But after playing with the 2>&1 thing I established that "mygoodcommand" needed all of its commands to be path specific too. In my case I was attempting to dump a processed uploaded spreadsheet to a database with the command:

mysql --local-infile -u supportadmin --password='*******' personnel < /Users/leenoble/Sites/Websites/Support/data/updateexec.sql

In order for this to work I had to add:

/usr/local/mysql/bin/ to the mysql command to make it work. I hope this helps stop someone else from tearing their hair out in frustration.
mk at neon1 dot net 20-Apr-2003 06:17
If you want to execute background processes from PHP that should run indefinitely, be aware of the following nasty behavior (confirmed with PHP 4.3.1 under FreeBSD, but probably under other flavors of UNIX, too):

PHP internally calls setitimer(2) to set the profiling interval timer (ITIMER_PROF) to enforce execution time limits (max_execution_time and max_input_time). These timer values are passed down to all processes executed by PHP. This means that after such a process has consumed [max_execution_time] seconds of CPU time (not wallclock time!), the system will send it a SIGPROF (signal 27). Since most processes don't use this signal and as such don't call signal(3) to catch or ignore it, the default action is executed, which is to terminate the process.

So if you see background processes that were executed from PHP dying at seemingly random times, you may be experiencing this issue. The solution is simply to call set_time_limit(0) just before executing the process.
jpgiot at ifrance.com 26-Jan-2003 03:30
FOR WINDOWS USERS

i had a look to start command. it's really usefull in fact.

this is how i launch a specific Apache SSL server

<?php
$cmd = "start /D C:\OpenSA\Apache /B Apache.exe -D SSL";
exec($cmd,$output,$rv);
?>

/D specify the path where application will be launched (equivalent to cd to path)
/B launch application without a console window

so to know the exact parameters of start, you could use

<?php
exec("start /? > start.txt");
?>

and you will get the help of start in a file named 'start.txt' in the same place you run the script

for WIN 98 you may need to modify a little your command

exec("COMMAND.COM /C START program args >NUL");

(taken from another post)
jfl at eksperten dot dk 10-Jan-2003 07:01
I made my script work in the background like this:
function start_shell ($cmd) {
    exec('nohup "'.$cmd.'" > /dev/null &');
}
qscripts at lycos dot nl 07-Jan-2003 02:45
Why not using the "start" utility, provided with every version of Windows to start processes in the background on Windows machines? For example :

exec("start song.mp3");

Which will cause the default handeling application for .MP3 file types to start playing the selected song..
NOtvdgeerSPAM at NOxs4allSPAM dot nl 03-Dec-2002 01:36
For users of PHP4 & Apache on Windows2000/XP:

If you're trying to execute a command-line application from PHP that has to show a (console) window on your desktop, make sure you enable the option to 'allow service to interact with desktop' in de service properties of Apache. (See your Windows services)

CAUTION: This can lead to security problems if your setting up a publicly available webserver!
k dot mitz dot NO_SPAM at att dot NO_SPAM dot net 15-Sep-2002 11:07
Newbie note:

The only syntax I found to work for the command portion of an an exec() call on a Win2K devel platform is:

$cmd = "\"path-to-exe\" args file-name";

where 'path-to-exe' has escaped double quotes, args are in the standard format, and 'file-name' has any backslashes escaped.

Example:

$cmd = "\"C:\program files\winzip\wzunzip.exe\" -c C:\\temp\\uploaded_file.zip";

exec($cmd,$output,$rv);

Note that the backslashes are escaped in the uploaded_file name, but not in the path to call the Winzip executable.  Go figure!
kop at meme dot com 12-Aug-2002 11:52
AFICT, the standard Unix Apache configuration causes an rare problem when running a job in the background. The MaxRequestsPerChild directive causes the child to terminate after 1000 requests, any background processes associated with the child will die with the child unless they are started with the "nohup" command.  Thus, the proper way to start a job in the background is to use:

exec('nohup my-command > /dev/null 2>&1 &')
ramirosuarez at fibertel dot com dot ar 13-Jul-2002 05:58
For Windows Users:

Keep in mind that a lot of UNABLE TO FORK Errors are the result of insufficient permissions.

CMD.EXE, TEMP Directory (or whatever you specified in php.ini), and all the directories that you use to upload o manipulate your files need to have Write privileges? usually user USER.

This will be useful for all the people who use GD Libraries or other programs that manipulate graphic images.
GCMXZPJPDJER at spammotel dot com 30-Jun-2002 09:41
to execute a script in background from php you don't need to use mikehup or other tools. just do:

`/usr/bin/php -q foobar.php >/dev/null 2>&1 &`;

mat
deschampsbest at noos dot fr 26-Jun-2002 10:05
I needed to know when a group of background tasks, which had been launched with a call to system, had terminated.
I could not find a function to call, so I created a little function.

It basically loops on the existance of a string in the results returned by the command ps.

All my commands, which run in background have the pid returned by posix_getpid in them.

I am able to launch many background task and effectively wait for them all to finish.

Before this, I would basically would sleep for N seconds.

I apologise if a well known or better method exist.

Thanks,
The New Bee
===============
===============

function wait_until_termination ($id, $duration){
                $i = 0;
                do {
                        $i += 1;

                        $cnt = `ps -auxww |
                                grep $id |
                                grep -v grep |
                                awk '{print $2}' |
                                grep -v $id|
                                wc -l` ;

                        if ($cnt > 0) {
                                sleep ($duration);
                        }

                } while ($cnt != 0);

                echo ("wait_until_termination (PID: $id, SEC: $duration) : LOOPS
:$i<BR>");
        }
rolland dot dudemaine at msg-software dot com 11-Apr-2002 02:45
In case you ever had to chain from php to another program (e.g. with a cgi php that only gives part of the output, or with php-gtk), here is a little C program that kills his parent (php, for instance), then launches a program given in argument.

chain.c :

#include <unistd.h>

int main(int argc, char**argv) {
  /* kill the parent */
  kill(getppid(), 15);
  argv++;
  /* then launch the new program */
  return execvp(argv[0], argv);
}
(compile with gcc -O3 -o chain chain.c)
then in php, use
<?
exec('chain sh -c echo test');
?>
vi_pa at hotmail dot com 05-Apr-2002 01:17
For those who want to execute a .php script to run in the background, from a
.php web page...

exec("php script.php parameters 2>dev/null >&- <&- >/dev/null &");

Where...
- php is the path to your php script executer (php has to be specifically complied to be to do this)
- script.php is the script
- parameters are none or more parameters
- 2>dev/null redirects the stderr to a file
- <&- switches off the stdin
- >&- switches off the stdout
- >dev/null redirects all other output to the file dev/null
- & direct script to run in background

This is the only way I managed to get it working (Linux & Apache, php 4x enviroment) . What is also great is that the process is forked so even though a user may close the browser that initiated the exec(), the process will still run to completion. And the dev/null file can be turned into a log.

What I found odd is that the script I was execing would run fine in the bg when executed from the command line, but not from the browser until I closed the stdin and stdout.
daniel dot hopp at godot dot de 01-Feb-2002 08:25
Re: session_write_close()

To launch a background process within a session, I recommend
to use a start-stop-daemon and ship parameters via ENV.

Example:
----------------------------------------
<?php
  // Within a session..
  exec("/some/where/launch.sh 300");
  // ..finished immediately.
?>

----------------------------------------
#!/bin/bash
# /some/where/launch.sh
T=$1
export T
DAEMON=/some/where/runme.pl
start-stop-daemon --start --quiet --background --exec $DAEMON

----------------------------------------
#!/usr/bin/perl
# /some/where/runme.pl
my $t = $ENV{'T'};
sleep($t);

----------------------------------------
edwin at bit dot nl 23-Jan-2002 12:47
If you are using sessions and want to start a background process, you might have the following problem:
The first time you call your script everything goes fine, but when you call it again and the process is STILL running, your script seems to "freeze" until you kill the process you started the first time.

You'll have to call session_write_close(); to solve this problem. It has something to do with the fact that only one script/process can operate at once on a session. (others will be lockedout until the script finishes)

I don't know why it somehow seems to be influenced by background processes, but I tried everything and this is the only solution. (i had a perl script that "daemonized" it's self like the example in the perl manuals)

Took me a long time to figure out, thanks ian@virtisp.net! :-)
lk1 at reglos dot de 25-Oct-2001 12:05
To keep a program running in the background on win98 the command
exec("COMMAND.COM /C START program args >NUL");
works fine for me.
naken at naken dot cc 15-Aug-2001 11:17
Anyone who still wants a copy of mikehup.c,
I rewrote it:  http://www.naken.cc/mikehup.php
This program will help you run programs in the
background that are called with the php system()
function.