# 2.9. Troubleshooting an Installation

## 2.9.1. First Install

If your CouchDB doesn’t start after you’ve just installed, check the following things:

- On UNIX-like systems, this is usually this is a permissions issue. Ensure that you’ve followed the User Registration and Security `chown`/`chmod` commands. This problem is indicated by the presence of the keyword `eacces` somewhere in the error output from CouchDB itself.
- Some Linux distributions split up Erlang into multiple packages. For your distribution, check that you really installed all the required Erlang modules. This varies from platform to platform, so you’ll just have to work it out for yourself. For example, on recent versions of Ubuntu/Debian, the `erlang` package includes all Erlang modules.
- Confirm that Erlang itself starts up with crypto (SSL) support:

    ## what version of erlang are you running? Ensure it is supported
    erl -noshell -eval 'io:put_chars(erlang:system_info(otp_release)).' -s erlang halt
    ## are the erlang crypto (SSL) libraries working?
    erl -noshell -eval 'case application:load(crypto) of ok -> io:put_chars("yay_crypto\n") ; _ -> exit(no_crypto) end.' -s init stop

- Next, identify where your Erlang CouchDB libraries are installed. This will typically be the lib/ subdirectory of the release that you have installed.
- Use this to start up Erlang with the CouchDB libraries in its path:

    erl -env ERL_LIBS $ERL_LIBS:/path/to/couchdb/lib -couch_ini -s crypto

- In that Erlang shell, let’s check that the key libraries are running. The `%%` lines are comments, so you can skip them:

    %% test SSL support. If this fails, ensure you have the OTP erlang-crypto library installed
    crypto:md5_init().

    %% test Snappy compression. If this fails, check your CouchDB configure script output or alternatively
    %% if your distro comes with erlang-snappy make sure you're using only the CouchDB supplied version
    snappy:compress("gogogogogogogogogogogogogogo").

    %% test the CouchDB JSON encoder. CouchDB uses different encoders in each release, this one matches
    %% what is used in 2.0.x.
    jiffy:decode(jiffy:encode(<<"[1,2,3,4,5]">>)).

    %% this is how you quit the erlang shell.
    q().

- The output should resemble this, or an error will be thrown:

    Erlang/OTP 17 [erts-6.2] [source] [64-bit] [smp:2:2] [async-threads:10] [kernel-poll:false]

    Eshell V6.2  (abort with ^G)
    1> crypto:md5_init().
    <<1,35,69,103,137,171,205,239,254,220,186,152,118,84,50,
      16,0,0,0,0,0,0,0,0,0,0,0,0,0,...>>
    2> snappy:compress("gogogogogogogogogogogogogogo").
    {ok,<<28,4,103,111,102,2,0>>}
    3> jiffy:decode(jiffy:encode(<<"[1,2,3,4,5]">>)).
    <<"[1,2,3,4,5]">>
    4> q().

- At this point the only remaining dependency is your system’s Unicode support library, ICU, and the Spidermonkey Javascript VM from Mozilla. Make sure that your `LD_LIBRARY_PATH` or equivalent for non-Linux systems (`DYLD_LIBRARY_PATH` on macOS) makes these available to CouchDB. Linux example running as normal user:

      LD_LIBRARY_PATH=/usr/local/lib:/usr/local/spidermonkey/lib couchdb

    Linux example running as couchdb user:

    echo LD_LIBRARY_PATH=/usr/local/lib:/usr/local/spidermonkey/lib couchdb | sudo -u couchdb sh

- If you receive an error message including the key word `eaddrinuse`, such as this:

      Failure to start Mochiweb: eaddrinuse

    edit your ``etc/default.ini`` or ``etc/local.ini`` file and change the
    ``[chttpd] port = 5984`` line to an available port.

- If you receive an error including the string:

    … OS Process Error … {os_process_error,{exit_status,127}}

then it is likely your SpiderMonkey JavaScript VM installation is not correct. Please recheck your build dependencies and try again.

- If you receive an error including the string:

    … OS Process Error … {os_process_error,{exit_status,139}}

this is caused by the fact that SELinux blocks access to certain areas of the file system. You must re-configure SELinux, or you can fully disable SELinux using the command:

    setenforce 0

- If you are still not able to get CouchDB to start at this point, keep reading.

## 2.9.2. Quick Build

Having problems getting CouchDB to run for the first time? Follow this simple procedure and report back to the user mailing list or IRC with the output of each step. Please put the output of these steps into a paste service (such as https://paste.apache.org/) rather than including the output of your entire run in IRC or the mailing list directly.

1. Note down the name and version of your operating system and your processor architecture.
2. Note down the installed versions of CouchDB’s dependencies.
3. Follow the checkout instructions to get a fresh copy of CouchDB’s trunk.
4. Configure from the couchdb directory:

    ./configure

5. Build the release:

    make release

6. Run the couchdb command and log the output:

    cd rel/couchdb
    bin/couchdb

7. Use your system’s kernel trace tool and log the output of the above command.
   1. For example, linux systems should use `strace`:

    strace bin/couchdb 2> strace.out

8. Report back to the mailing list (or IRC) with the output of each step.

## 2.9.3. Upgrading

Are you upgrading from CouchDB 2.0? Install CouchDB into a fresh directory. CouchDB’s directory layout has changed and may be confused by libraries present from previous releases.

## 2.9.4. Runtime Errors

### Lots of memory being used on startup

Is your CouchDB using a lot of memory (several hundred MB) on startup? This one seems to especially affect Dreamhost installs. It’s really an issue with the Erlang VM pre-allocating data structures when ulimit is very large or unlimited. A detailed discussion can be found on the erlang-questions list, but the short answer is that you should decrease `ulimit -n` or define `ERL_MAX_PORTS` to something reasonable like 1024.

### erlang stack trace contains `system_limit`, `open_port`

Erlang has a default limit of 1024 ports, where each FD, tcp connection, and linked-in driver uses one port. You seem to have exceeded this. You can change it at runtime using the `ERL_MAX_PORTS` env variable.

### function raised exception (Cannot encode ‘undefined’ value as JSON)

If you see this in the CouchDB error logs, the JavaScript code you are using for either a map or reduce function is referencing an object member that is not defined in at least one document in your database. Consider this document:

    {
      "_id":"XYZ123",
      "_rev":"1BB2BB",
      "field":"value"
    }

and this map function:

    function(doc) {
      emit(doc.name, doc.address);
    }

This will fail on the above document, as it does not contain a `name` or `address` member. Instead, use guarding to make sure the function only accesses members when they exist in a document:

    function(doc) {
      if(doc.name && doc.address) {
        emit(doc.name, doc.address);
      }
    }

While the above guard will work in most cases, it’s worth bearing JavaScript’s understanding of ‘false’ values in mind. Testing against a property with a value of 0 (zero), `''` (empty String), `false` or `null` will return false. If this is undesired, a guard of the form `if (doc.foo !== undefined)` should do the trick.

This error can also be caused if a reduce function does not return a value. For example, this reduce function will cause an error:

    function(key, values) {
      sum(values);
    }

The function needs to return a value:

    function(key, values) {
      return sum(values);
    }

### erlang stack trace contains `bad_utf8_character_code`

CouchDB 1.1.1 and later contain stricter handling of UTF8 encoding. If you are replicating from older versions to newer versions, then this error may occur during replication.

A number of work-arounds exist; the simplest is to do an in-place upgrade of the relevant CouchDB and then compact prior to replicating.

Alternatively, if the number of documents impacted is small, use filtered replication to exclude only those documents.