Topic: /dev/mem access from phpextension (from .so file)

[linto.thomas]

I need to write some configuration to hardware by accessing /dev/mem from apache but the function 'open("/dev/mem",O_RDWR)' in php extension returns '-1' ,permission denied

if any body knows how to solve this problem please help

thanks in advance

linto

[James Blond]

I guess the apache process has no rights / permission to write to it. Which chmod has /dev/mem ?

[linto.thomas]

-bash-4.2# ls -l /dev/mem*
crw-r----- 1 root kmem 1, 1 Dec 31 19:00 /dev/mem

I add a user www and add the user in root ,kmem,wheel groups .

if i log in as www and run a sample C code to open it will work . the same user is used in httpd.conf

[James Blond]

Open yes, but the group is only allowed to read, not to write. So you should allow the group to write!

[linto.thomas]

but open itself return -1

[James Blond]

-1 is false. So it does not seem to work.

You might try to get a better error message.

[linto.thomas]

I also use the same code and the handle fd returns -1

[James Blond]

I googled a bit and found out that the linux kernel disables the access to /dev/mem for non root users

google CONFIG_STRICT_DEVMEM

So I think you have to find another way to access the memory. maybe mmap ? See also the proved answer in http://stackoverflow.com/questions/647783/direct-memory-access-in-linux

[linto.thomas]

error value 22
EINVAL

[James Blond]

I think you should ask a linux kernel guy about that.