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 MEMCACHED(1)                                                   MEMCACHED(1)
                               April 11, 2005

      memcached - high-performance memory object caching system

      memcached [options]

      This manual page documents briefly the memcached memory object caching

      memcached is a flexible memory object caching daemon designed to
      alleviate database load in dynamic web applications by storing objects
      in memory.  It's based on libevent to scale to any size needed, and is
      specifically optimized to avoid swapping and always use non-blocking

      These programs follow the usual GNU command line syntax. A summary of
      options is included below.

      -s, --unix-socket=<file>
           Unix socket path to listen on (disables network support).

      -A, --enable-shutdown
           Enable ascii "shutdown" command.

      -a, --unix-mask=<perms>
           Permissions (in octal format) for Unix socket created with -s

      -l, --listen=<addr>
           Listen on <addr>; default to INADDR_ANY. <addr> may be specified
           as host:port.  If you don't specify a port number, the value you
           specified with -p or -U is used. You may specify multiple
           addresses separated by comma or by using -l multiple times. This
           is an important option to consider as there is no other way to
           secure the installation. Binding to an internal or firewalled
           network interface is suggested.

      -d, --daemon
           Run memcached as a daemon.

      -u, --user=<username>
           Assume the identity of <username> (only when run as root).

      -m, --memory-limit=<num>
           Use <num> MB memory max to use for object storage; the default is
           64 megabytes.

      -c, --conn-limit=<num>
           Use <num> max simultaneous connections; the default is 1024.

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      -R, --max-reqs-per-event=<num>
           This option seeks to prevent client starvation by setting a limit
           to the number of sequential requests the server will process from
           an individual client connection. Once a connection has exceeded
           this value, the server will attempt to process I/O on other
           connections before handling any further request from this
           connection. The default value for this option is 20.

      -k, --lock-memory
           Lock down all paged memory. This is a somewhat dangerous option
           with large caches, so consult the README and memcached homepage
           for configuration suggestions.

      -p, --port=<num>
           Listen on TCP port <num>, the default is port 11211.

      -U, --udp-port=<num>
           Listen on UDP port <num>, the default is port 11211, 0 is off.

      -M, --disable-evictions
           Disable automatic removal of items from the cache when out of
           memory.  Additions will not be possible until adequate space is
           freed up.

      -r, --enable-coredumps
           Raise the core file size limit to the maximum allowable.

      -f, --slab-growth-factor=<factor>
           Use <factor> as the multiplier for computing the sizes of memory
           chunks that items are stored in. A lower value may result in less
           wasted memory depending on the total amount of memory available
           and the distribution of item sizes.  The default is 1.25.

      -n, --slab-min-size=<size>
           Allocate a minimum of <size> bytes for the item key, value, and
           flags. The default is 48. If you have a lot of small keys and
           values, you can get a significant memory efficiency gain with a
           lower value. If you use a high chunk growth factor (-f option),
           on the other hand, you may want to increase the size to allow a
           bigger percentage of your items to fit in the most densely packed
           (smallest) chunks.

      -C, --disable-cas
           Disable the use of CAS (and reduce the per-item size by 8 bytes).

      -h, --help
           Show the version of memcached and a summary of options.

      -v, --verbose
           Be verbose during the event loop; print out errors and warnings.

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      -vv  Be even more verbose; same as -v but also print client commands
           and responses.

      -vvv Be extremely verbose; same of the above and also print internal
           state transitions.

      -i, --license
           Print memcached and libevent licenses.

      -P, --pidfile=<filename>
           Print pidfile to <filename>, only used under -d option.

      -t, --threads=<threads>
           Number of threads to use to process incoming requests. This
           option is only meaningful if memcached was compiled with thread
           support enabled. It is typically not useful to set this higher
           than the number of CPU cores on the memcached server. Setting a
           high number (64 or more) of worker threads is not recommended.
           The default is 4.

      -D <char>
           Use <char> as the delimiter between key prefixes and IDs. This is
           used for per-prefix stats reporting. The default is ":" (colon).
           If this option is specified, stats collection is turned on
           automatically; if not, then it may be turned on by sending the
           "stats detail on" command to the server.

      -L, --enable-largepages
           Try to use large memory pages (if available). Increasing the
           memory page size could reduce the number of TLB misses and
           improve the performance. In order to get large pages from the OS,
           memcached will allocate the total item-cache in one large chunk.
           Only available if supported on your OS.

      -b, --listen-backlog=<num>
           Set the backlog queue limit to <num> connections. The default is

      -B, --protocol=<proto>
           Specify the binding protocol to use.  By default, the server will
           autonegotiate client connections.  By using this option, you can
           specify the protocol clients must speak.  Possible options are
           "auto" (the default, autonegotiation behavior), "ascii" and

      -I, --max-item-size=<size>
           Override the default size of each slab page. The default size is
           1mb. Default value for this parameter is 1m, minimum is 1k, max
           is 128m.  Adjusting this value changes the item size limit.

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      -S, --enable-sasl
           Turn on SASL authentication. This option is only meaningful if
           memcached was compiled with SASL support enabled.

      -F, --disable-flush-all
           Disables the "flush_all" command. The cmd_flush counter will
           increment, but clients will receive an error message and the
           flush will not occur.

      -X, --disable-dumping
           Disables the "stats cachedump" and "lru_crawler metadump"

      -o, --extended=<options>
           Comma separated list of extended or experimental options. See -h
           or wiki for up to date list.

      -V, --version
           print version and exit

      The memcached daemon is copyright Danga Interactive and is distributed
      under the BSD license. Note that daemon clients are licensed

      The README file that comes with memcached

      The memcached daemon was written by Anatoly Vorobey <>
      and Brad Fitzpatrick <> and the rest of the crew of
      Danga Interactive

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