Updating OpenBSD section of doc/TUNING.

doc/TUNING

@@ -38,62 +38,41 @@ read-only on OS X.
 OpenBSD
 -------
 
-For recent versions of OpenBSD (5.5 and 5.6, and probably older releases
-as well), the maximum number of file descriptors that can be opened is
-7030:
+Because OpenBSD is primarily focused on security and stability, it uses default
+resource limits stricter than those of more popular Unix-like operating systems.
 
-http://unix.stackexchange.com/questions/104929/does-openbsd-have-a-limit-to-the-number-of-file-descriptors/104948#104948
+OpenBSD stores a kernel-level file descriptor limit in the sysctl variable
+kern.maxfiles. It defaults to 7,030. To change it to, for example, 16,000 while
+the system is running, use the command 'sudo sysctl kern.maxfiles=16000'.
+kern.maxfiles will reset to the default value upon system reboot unless you also
+add 'kern.maxfiles=16000' to the file /etc/sysctl.conf.
 
-The maximum number of file descriptors that an OpenBSD machine can have
-open is stored in the sysctl variable kern.maxfiles. This value defaults
-to 7030 - to verify this, run sysctl kern.maxfiles.
+There are stricter resource limits set on user classes, which are stored in
+/etc/login.conf. This config file also allows limit sets for daemons started
+with scripts in the /etc/rc.d directory, which presumably includes Tor.
 
-To immediately change a running system's file descriptor limit to, for
-example, 20,000 files, run sudo sysctl kern.maxfiles=20000. All sysctl
-variables are reset upon reboot using defaults and /etc/sysctl.conf, so
-to make your change permanent you must add the line kern.maxfiles=20000
-to /etc/sysctl.conf.
-
-One can also change a maximum number of allowed file descriptors for Tor
-daemon alone by editing /etc/rc.d/tor and adding the following lines:
+To increase the file descriptor limit from its default of 1,024, add the
+following to /etc/login.conf:
 
 tor:\
-        :openfiles-max=8192:\
-        :tc=daemon:
-
-However, there are stricter limits set on users. This is a security
-feature intended to prevent one user from choking out others by opening
-all possible file descriptors.
-
-The stricter limits are set in /etc/login.conf. This config file sets
-resource access rules for user classes. You should be running
-Tor as a non-privileged daemon user '_tor', which belongs to the 'daemon'
-class. It will therefore be subject to the 'default' and 'daemon' rules.
-There are two relevant rules: openfiles-cur and openfiles-max. The prior
-is the initial limit upon login - the soft limit. The latter is the maximum
-limit that can be set using 'ulimit -n' or setrlimit() without editing
-/etc/login.conf and rebooting. This is known as the hard limit.
-
-Without editing /etc/login.conf, daemon-owned processes have
-soft limit of 512 open files and a hard limit of 1024 open files.
-Tor can increase the soft limit as needed, so you will therefore
-eventually get warnings about running out of available file descriptors
-once Tor reaches ~1024 open files.
-
-To increase the hard limit, add the following line to the daemon class
-rules in /etc/login.conf:
+	:openfiles-max=13500:\
+	:tc=daemon:
 
-tor:\
-        :openfiles-max=8192:\
-        :tc=daemon:
+Upon restarting Tor, it will be able to open up to 13,500 file descriptors.
+
+This will work *only* if you are starting Tor with the script /etc/rc.d/tor. If
+you're using a custom build instead of the package, you can easily copy the rc.d
+script from the Tor port directory. Alternatively, you can ensure that the Tor's
+daemon user has its own user class and make a /etc/login.conf entry for it.
+
+High-bandwidth relays sometimes give the syslog warning:
 
-Upon restarting the machine, Tor will be able to open up to 6500 file
-descriptors.
+/bsd: WARNING: mclpools limit reached; increase kern.maxclusters
 
-Be aware that, by doing this, you are bypassing a security and stability
-feature of the OS. If you are running your relay on a weak or old system,
-watch your system load to ensure that it can handle this many open files.
-Also, Tor may interfere with any other programs that open many files.
+In this case, increase kern.maxclusters with the sysctl command and in the file
+/etc/sysctl.conf, as described with kern.maxfiles above. Use 'sysctl
+kern.maxclusters' to query the current value. Increasing by about 15% per day
+until the error no longer appears is a good guideline.
 
 Disclaimer
 ----------