Homebrew Postgresql Service not Starting Resolved

Published 01 Oct 2022 · 6 min read
Learn why your postgresql homebrew service won't start and how to fix it.

This post will cover how to troubleshoot when the postgresql service installed via Homebrew on a Mac isn't starting. If you work on a Mac, it's likely you use Homebrew to install packages. In addition to installing, you can also manage services using Homebrew's services subcommand, a wrapper for launchctl. A common usage of the services subcommand is to start and stop databases.

What's Running

This all started when I wanted to follow along with a Rails tutorial that required scaffolding a new project with Postgresql as the database. For production projects, I prefer to setup all databases in Docker containers, but for a simple tutorial, it's fine to use a local service, which I had installed some time ago via brew install postgresql.

However, I couldn't remember whether the database server was running. To get information about services that are currently being managed by Homebrew, use the list option of the services subcommand:

brew services list

My output showed I had mysql, postgresql, and redis as managed services, but that postgres wasn't started:

mysql      started dbaron ~/Library/LaunchAgents/homebrew.mxcl.mysql.plist
postgresql none
redis      started dbaron ~/Library/LaunchAgents/homebrew.mxcl.redis.plist

So the fix should be simple enough, just start it with the start option of the services subcommand:

brew services start postgresql

The output of this command showed it was successful:

==> Successfully started `postgresql` (label: homebrew.mxcl.postgresql)

The Problem

But before pressing the easy button for finding such a quick fix, I wanted to check that a connection worked. PostgreSQL comes with psql, a command line tool to interact with the database. You can connect to the default postgres database as follows:

psql -d postgres

Unfortunately, the output of this command showed the database was not running:

psql: error: connection to server on socket "/tmp/.s.PGSQL.5432" failed: No such file or directory
Is the server running locally and accepting connections on that socket?

A further check with lsof (list open files belonging to active processes) confirmed there was no process listening on port 5432, which is the default port used by postgresql. The -nP options indicate not to include host and port names in the Node Name column and +c 15 increases the command width display, which otherwise defaults to 9:

lsof -nP +c 15 | grep LISTEN
# no output for 5432

So much for the easy button.

Debugging

The info command can be used to get more detailed information about a specific service. Running it for postgresql:

brew services info postgresql

The output shows that the postgresql service is loaded, but not running:

postgresql (homebrew.mxcl.postgresql)
Running: ✘
Loaded: ✓
Schedulable: ✘

The brew services list command can be used again, but this time, instead of showing none for postgresql, it shows an error status and path to a plist file (because of the earlier attempt to start it which failed):

$ brew services list
Name       Status     User   File
mysql      started    dbaron ~/Library/LaunchAgents/homebrew.mxcl.mysql.plist
postgresql error  256 dbaron ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist
redis      started    dbaron ~/Library/LaunchAgents/homebrew.mxcl.redis.plist

The .plist files contain service configuration information. Let's take a look at the configuration for the postgresql service:

cat ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist

The output shows that it's an xml file:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
  <dict>
    <key>KeepAlive</key>
    <true />
    <key>Label</key>
    <string>homebrew.mxcl.postgresql</string>
    <key>ProgramArguments</key>
    <array>
      <string>/usr/local/opt/postgresql/bin/postgres</string>
      <string>-D</string>
      <string>/usr/local/var/postgres</string>
    </array>
    <key>RunAtLoad</key>
    <true />
    <key>StandardErrorPath</key>
    <string>/usr/local/var/log/postgres.log</string>
    <key>StandardOutPath</key>
    <string>/usr/local/var/log/postgres.log</string>
    <key>WorkingDirectory</key>
    <string>/usr/local</string>
  </dict>
</plist>

Notice that one of the values is a path to an error file (actually its the same file used for both standard out and standard error) - /usr/local/var/log/postgres.log. Let's take a look at this file to see if it has any clues as to why postgresql isn't starting:

$ cat /usr/local/var/log/postgres.log
2022-06-16 15:15:04.193 EDT [69330] FATAL:  database files are incompatible with server
2022-06-16 15:15:04.193 EDT [69330] DETAIL:  The data directory was initialized by PostgreSQL version 13, which is not compatible with this version 14.3.

Aha, a version incompatibility error! To confirm the version of the currently installed service:

$ psql --version
psql (PostgreSQL) 14.3

Solution

When the Postgres data directory was first created, I must have been on older Postgres version 13, and at some point updated the brew formula to 14. This version mismatch makes postgresql fail to start. Fortunately, there's a homebrew command that can be run to migrate the data from a previous major version:

brew postgresql-upgrade-database

There will be a lot of output from this command, but here are some highlights of what it does:

brew install postgresql@13
...
Upgrading postgresql data from 13 to 14..
...
Moving postgresql data from /usr/local/var/postgres to /usr/local/var/postgres.old...
...
Migrating and upgrading data...
...
==> Upgraded postgresql data from 13 to 14!
==> Your postgresql 13 data remains at /usr/local/var/postgres.old
==> Successfully started `postgresql` (label: homebrew.mxcl.postgresql)

It installs the previous major version of postgresql (in my case, I was on 14 so previous major was 13), migrates, backs up the current data directory to .old, then migrates the data to the new major version. The idea being if something goes wrong with data migration, you can still access your old data with the previous major.

Finally this command also starts up the current/latest version of the service. Let's confirm its started:

$ brew services list
Name       Status     User   File
mysql      started    dbaron ~/Library/LaunchAgents/homebrew.mxcl.mysql.plist
postgresql started    dbaron ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist
redis      started    dbaron ~/Library/LaunchAgents/homebrew.mxcl.redis.plist

And re-run the lsof command from earlier to confirm there's a postgres process listening on 5432:

lsof -nP +c 15 | grep LISTEN

Output includes postgres, so far so good:

COMMAND          PID   USER   FD      TYPE             DEVICE  SIZE/OFF    NODE NAME
postgres        1788 dbaron    7u     IPv6 0x696b8fad0ce2d7bd       0t0    TCP [::1]:5432 (LISTEN)
...

Last check is to ensure we can connect:

$ psql -d postgres
psql (14.2)
Type "help" for help.

postgres=#

This time the psql connection command goes to the postgres prompt, which means connection could be established, success!

Conclusion

This post has walked through how to fix an issue with the postgresql service not starting on a Mac when managed by homebrew. In general when debugging homebrew services, use the brew services list command to get information about managed services and their plist files which contain configuration for the service. Then inspect the contents of the plist file to see if it specifies any log files. Then check the log file(s) for reason why service won't start and fix that.