Command not found error on apache version 2.2.3 in CentOs

[Daniel Requena <daniel@xxxxxxxxxxxxxx>]

Hi,
when I try to execute a php order using shell_exec or backtick  
operator, the command never returns anything. Also, appears a new line  
in error_log file each time php file is called from url, with the next  
information:
sh: hostname: command not found.
I've tried to put the complete path when calling `hostname` command,  
using echo `/bin/hostname` php order, and then appears the next error  
in error_log:
sh: hostname: permission denied
The user apache is well-configurd in system and pointed in httpd.conf  
file as
User apache
Group apache
Can anyone help me?
Many thanks,

Dani

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