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@@ -35,6 +35,66 @@ when it launches tor service (see launchd.plist(5) manpage). Also,
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kern.ipc.maxsockets is determined dynamically by the system and thus is
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read-only on OS X.
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+OpenBSD
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+-------
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+
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+For recent versions of OpenBSD (5.5 and 5.6, and probably older releases
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+as well), the maximum number of file descriptors that can be opened is
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+7030:
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+
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+http://unix.stackexchange.com/questions/104929/does-openbsd-have-a-limit-to-the-number-of-file-descriptors/104948#104948
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+
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+The maximum number of file descriptors that an OpenBSD machine can have
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+open is stored in the sysctl variable kern.maxfiles. This value defaults
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+to 7030 - to verify this, run sysctl kern.maxfiles.
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+
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+To immediately change a running system's file descriptor limit to, for
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+example, 20,000 files, run sudo sysctl kern.maxfiles=20000. All sysctl
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+variables are reset upon reboot using defaults and /etc/sysctl.conf, so
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+to make your change permanent you must add the line kern.maxfiles=20000
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+to /etc/sysctl.conf.
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+
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+One can also change a maximum number of allowed file descriptors for Tor
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+daemon alone by editing /etc/rc.d/tor and adding the following lines:
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+
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+tor:\
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+ :openfiles-max=8192:\
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+ :tc=daemon:
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+
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+However, there are stricter limits set on users. This is a security
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+feature intended to prevent one user from choking out others by opening
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+all possible file descriptors.
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+
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+The stricter limits are set in /etc/login.conf. This config file sets
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+resource access rules for user classes. You should be running
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+Tor as a non-privileged daemon user '_tor', which belongs to the 'daemon'
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+class. It will therefore be subject to the 'default' and 'daemon' rules.
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+There are two relevant rules: openfiles-cur and openfiles-max. The prior
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+is the initial limit upon login - the soft limit. The latter is the maximum
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+limit that can be set using 'ulimit -n' or setrlimit() without editing
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+/etc/login.conf and rebooting. This is known as the hard limit.
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+
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+Without editing /etc/login.conf, daemon-owned processes have
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+soft limit of 512 open files and a hard limit of 1024 open files.
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+Tor can increase the soft limit as needed, so you will therefore
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+eventually get warnings about running out of available file descriptors
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+once Tor reaches ~1024 open files.
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+
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+To increase the hard limit, add the following line to the daemon class
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+rules in /etc/login.conf:
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+
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+tor:\
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+ :openfiles-max=8192:\
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+ :tc=daemon:
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+
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+Upon restarting the machine, Tor will be able to open up to 6500 file
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+descriptors.
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+
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+Be aware that, by doing this, you are bypassing a security and stability
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+feature of the OS. If you are running your relay on a weak or old system,
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+watch your system load to ensure that it can handle this many open files.
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+Also, Tor may interfere with any other programs that open many files.
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+
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Disclaimer
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----------
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Nick Mathewson