Wikipedia’s article related to procfs describes it as follows:
procfs (or the proc filesystem) is a special filesystem in Unix-like operating systems that presents information about processes and other system information in a hierarchical file-like structure, providing a more convenient and standardized method for dynamically accessing process data held in the kernel than traditional tracing methods or direct access to kernel memory.
Linux Kernel version 3.3 initially introduced the hidepid mount option for procfs quite some time ago but its usage isn’t always implemented. CentOS 6.3 and above have since offered full support for its usage. In the past the kernel source fs/proc/base.c needed to manually be patched with the line below to achieve the same capability:
inode->i_mode = S_IFDIR|S_IRUSR|S_IXUSR;
The following options can be defined for hidepid:
hidepid=0: Disable hidepid.
hidepid=1: Users other than root are only capable of realising information regarding their own processes but can still manually inspect /proc to gather references such as Process IDs.
hidepid=2: The ideal setting which will ensure privacy of /proc amongst standard users.
One factor to keep in mind is hidepid will not protect actual processes which do exist – it serves to only make process information more private.
Aside from modifying the system’s fstab, hidepid can be activated at runtime by remounting /proc as follows:
mount -o remount,hidepid=2 /proc