exec doesn't found a file

I'm having problems with the exec php function. When I do:

ls -al /dev/sdf1  

This doesn't found the archive (ls: cannot access /dev/sdf1: No such file or directory), but if I run this command, in console that show me the information. What can I do? That happen even running the php script as a root!!

$mountcommand = "ls -al /dev/$unit  2>&1";
exec("$mountcommand", &$mountoutput, &$mountresult);
print_r($mountoutput);
echo "\n$m开发者_运维百科ountcommand\n\n";

This is in a forked process

Works for me.

The disks:

frayser@gentoo ~/doc/Answers/src/PHP $ disk

sda     111.790 GB
sdb     233.762 GB
sdc     233.762 GB
sdd     233.762 GB
sde     279.481 GB
------------------
Total:  1092.558 GB

Using hde:

frayser@gentoo ~/doc/Answers/src/PHP $ l /dev/sde
brw-rw---- 1 root disk 8, 64 Dec  2 13:36 /dev/sde

Using PHP:

frayser@gentoo ~/doc/Answers/src/PHP $ php lsdev.php 
Z: brw-rw---- 1 root disk 8, 64 Dec  2 13:36 /dev/sde

The script:

frayser@gentoo ~/doc/Answers/src/PHP $ cat lsdev.php 
<?php
$z=exec("ls -lr /dev/sde");
print "Z: " . $z . "\n";
?>

Update

It also works with ls -al. Please show your script.

Update 2

Along the lines of the chroot suggestion by ircmaxell: Supposing that /dev, as seen in the PHP process, was a special chroot facsimile of the real one. And supposing that /dev/sdf1 is a removable device. The when sdf1(the media) is inserted the system automatically creates the device in the real /dev; but the chroot version isn't updated. So, to detect this situation look for differences between /dev as seen from PHP and from the commandline.

One test is ls -id on /dev(from PHP and the commandline). This prints the inode of /dev. Is there a mismatch in inode numbers?

Is /dev/sdf1 removable? Is it mounted? If it is mounted; does the PHP process see the mounted filesystem: ls $mount_point from PHP it.

There are other chroot tests listed on Stack Overflow and elsewhere; but I haven found many good ones: If a chroot is done correctly, it is hard to detect.

Update 3

This may be what is happening: The device (/dev/sdf1) takes a while to appear after it is created; so it is necessary to pause between creating the device and attempting to mount it:

Before: The device is created; but it isn't there...

Array
(
    [0] => Logging out of session [sid: 4, target: iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e, portal: 172.16.0.1,3260]
    [1] => Logout of [sid: 4, target: iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e, portal: 172.16.0.1,3260]: successful
    [2] => Logging in to [iface: iface0, target: iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e, portal: 172.16.0.1,3260]
    [3] => Login to [iface: iface0, target: iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e, portal: 172.16.0.1,3260]: successful
    [4] => ls: cannot access /dev/sdg: No such file or directory
)

{ test -b /dev/sdg && sudo iscsiadm -m node -T iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e -u; sudo iscsiadm -m node -T iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e -l; ls -al /dev/sdg ;} 2>&1

After: Added a 1-second pause, and the device (sdg) is available...

Array
(
    [0] => Logging out of session [sid: 5, target: iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e, portal: 172.16.0.1,3260]
    [1] => Logout of [sid: 5, target: iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e, portal: 172.16.0.1,3260]: successful
    [2] => Logging in to [iface: iface0, target: iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e, portal: 172.16.0.1,3260]
    [3] => Login to [iface: iface0, target: iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e, portal: 172.16.0.1,3260]: successful
    [4] => brw-rw---- 1 root disk 8, 96 Dec 18 05:27 /dev/sdg
)

{ test -b /dev/sdg && sudo iscsiadm -m node -T iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e -u; sudo iscsiadm -m node -T iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e -l; sleep 1; ls -al /dev/sdg ;} 2>&1

The PHP with the pause ...

<pre>
<?php
$unit='sdg';
$reset="test -b /dev/sdg && sudo iscsiadm -m node -T iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e -u";

$connect="sudo iscsiadm -m node -T iqn.2004-08.org.frayser:gen2-dummy.ad4s0.dos.e -l";

$test="ls -al /dev/$unit";

$mountcommand = "{ $reset; $connect; sleep 1; $test ;} 2>&1";
exec("$mountcommand", $mountoutput, $mountresult);
print_r($mountoutput); 
echo "\n$mountcommand\n\n";
?>
</pre>

The /etc/sudoers is configured the same as reported in the previous question about mount failing from PHP.

So add a second or two of sleep() after iscsiadm creates the device. The sleep can be done in PHP instead of in the exec() of the shell.

I fix it with a sleep between this code and the code that gave me the "unit"