Procfs

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Since time immemorial, tools like <tt>ps</tt> have enumerated processes via walking procfs's dentries when possible.

procfs since Linux 3.3 accepts a mount option <tt>hidepid</tt>, taking one of ~~three~~ values:

procfs since Linux 3.3 accepts a mount option <tt>hidepid</tt>, taking one of four values:

* 0: everyone may access all <tt>proc/PID</tt> directories

* 1: users can only access their own <tt>proc/PID</tt> directories

* 2: users can only *see* their own <tt>proc/PID</tt> directories

* 4: users can only see directories of processes they can [[ptrace]]

Linux 3.3 also introduced the <tt>gid</tt> parameter, which specifies a group ID. Members of this group are exempted from <tt>hidepid</tt> restrictions.

Note that if you start a process as one user, and change to another user using e.g. <tt>setuid(2)</tt>, you might no longer be able to access your own <tt>/proc/PID</tt>.

===<tt>proc/PID/loginuid</tt>===

Note that this is only present when <tt>CONFIG_AUDIT</tt> is enabled in the kernel configuration. Audit doesn't have to be enabled, and auditd doesn't need to be running, but without that option, no <tt>loginuid</tt> for you.

===<tt>proc/PID/stat</tt> sucks===

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</pre>

Unfortunately, <tt>proc/PID/status</tt> cheerfully leaves out several fields from <tt>stat</tt>, including <tt>flags</tt>, so it's like what was the point of that exactly. Ugh.

Unfortunately, <tt>proc/PID/status</tt> cheerfully leaves out several fields from <tt>stat</tt>, including <tt>flags</tt> and all the timing information, so it's like what was the point of that exactly. Ugh.

==See Also==

* The [[sysfs]] page

* UNIX V8 [http://man.cat-v.org/unix_8th/4/proc proc(4)] man page

Procfs: Difference between revisions

Dank (talk | contribs)

@@ Line 13: / Line 13: @@
 Since time immemorial, tools like <tt>ps</tt> have enumerated processes via walking procfs's dentries when possible.
-procfs since Linux 3.3 accepts a mount option <tt>hidepid</tt>, taking one of three values:
+procfs since Linux 3.3 accepts a mount option <tt>hidepid</tt>, taking one of four values:
 * 0: everyone may access all <tt>proc/PID</tt> directories
 * 1: users can only access their own <tt>proc/PID</tt> directories
 * 2: users can only *see* their own <tt>proc/PID</tt> directories
+* 4: users can only see directories of processes they can [[ptrace]]
 Linux 3.3 also introduced the <tt>gid</tt> parameter, which specifies a group ID. Members of this group are exempted from <tt>hidepid</tt> restrictions.
+Note that if you start a process as one user, and change to another user using e.g. <tt>setuid(2)</tt>, you might no longer be able to access your own <tt>/proc/PID</tt>.
+===<tt>proc/PID/loginuid</tt>===
+Note that this is only present when <tt>CONFIG_AUDIT</tt> is enabled in the kernel configuration. Audit doesn't have to be enabled, and auditd doesn't need to be running, but without that option, no <tt>loginuid</tt> for you.
 ===<tt>proc/PID/stat</tt> sucks===
@@ Line 84: / Line 90: @@
 </pre>
-Unfortunately, <tt>proc/PID/status</tt> cheerfully leaves out several fields from <tt>stat</tt>, including <tt>flags</tt>, so it's like what was the point of that exactly. Ugh.
+Unfortunately, <tt>proc/PID/status</tt> cheerfully leaves out several fields from <tt>stat</tt>, including <tt>flags</tt> and all the timing information, so it's like what was the point of that exactly. Ugh.
 ==See Also==
 * The [[sysfs]] page
 * UNIX V8 [http://man.cat-v.org/unix_8th/4/proc proc(4)] man page