php exec giving permission denied error

[newbie14]

Dear All,
I have a java application which send sms. So on console it works fine no problem. The problem comes when I start to run from the web browser using the php exec method. Then I get error as "PortInUseException : java.lang.RuntimeException:
Error opening "/dev/ttyUSB0"
Permission denied".
I guess I must do some permission settings in linux any help please? Thank you.

[zombykillah]

Well it seems that the user of executing the php doesn't have the rights to open the USB Device.
On my system the user would be "www-data".

To get the user you simply ask your system:
ps -ef | grep apache
for example

However you should take a look what user / groups have the rights to open the device:

ls -al /dev/ttyUSB0

As far as i know it should be enough to add the user executing the php into the group.
A typical code to do this would be:

usermod -a -G dialout www-data

[newbie14]

Dear Zom,
Ok first I ran this

ps -ef | grep apache
apache 3025 2940 0 04:40 ? 00:00:00 /usr/sbin/httpd
apache 3027 2940 0 04:40 ? 00:00:00 /usr/sbin/httpd
apache 3029 2940 0 04:40 ? 00:00:00 /usr/sbin/httpd
apache 3030 2940 0 04:40 ? 00:00:00 /usr/sbin/httpd
apache 3032 2940 0 04:40 ? 00:00:00 /usr/sbin/httpd
apache 3033 2940 0 04:40 ? 00:00:00 /usr/sbin/httpd
apache 3034 2940 0 04:40 ? 00:00:00 /usr/sbin/httpd
apache 3035 2940 0 04:40 ? 00:00:00 /usr/sbin/httpd
root 3365 3260 0 04:52 pts/1 00:00:00 grep apache

Thus the user here is known as apache.
Then I run this

ls -al /dev/ttyUSB0
crw-rw---- 1 root uucp 188, 0 Jan 1 04:44 /dev/ttyUSB0

Then I tried

usermod -a -G dialout apache
usermod: unknown group dialout

So what is my mistake ? Thank you.

[zombykillah]

usermod -a -G uucp apache

[newbie14]

Dear Zom,
Thank you it works now. Actually what is this command means ?

[zombykillah]

usermod
Is to change existing users
-a (add)
-G (Group)
uucp (Groupname)
apache (User that shall be modified)

ls -al /dev/ttyUSB0
Simply shows a line what user owns the device and what group has what rights to access:
crw-rw---- 1 root uucp 188, 0 Jan 1 04:44 /dev/ttyUSB0
Simply put:
root owns it
Members of Group uucp also have rw permission
anyone else has no permission
rw-rw----
The first 3 letters are for the owner, the second are the group and the last 3 is the rest.
You could also have solved it by allowing everyone to access the device (chmod).
Or you could have changed the owner or group with chown or chgrp.
But since it's a device I don't know if the system will remember such settings.

If you need more details you can access the manuals by writing:
man <command>
man usermod