I just reinstalled postgres via brew install postgres

I ran initdb /usr/local/var/postgres -E utf8 but got this:

The files belonging to this database system will be owned by user "atal421". This user must also own the server process. The database cluster will be initialized with locale "en_US.UTF-8". The default text search configuration will be set to "english". initdb: directory "/usr/local/var/postgres" exists but is not empty If you want to create a new database system, either remove or empty the directory "/usr/local/var/postgres" or run initdb with an argument other than "/usr/local/var/postgres". 

so, I rm -rf the postgres folder and ran it again:

 initdb /usr/local/var/postgres -E utf8 

it said everything was okay:

Success. You can now start the database server using: postgres -D /usr/local/var/postgres 

so, I ran that command and got:

postgres -D /usr/local/var/postgres FATAL: lock file "postmaster.pid" already exists HINT: Is another postmaster (PID 13731) running in data directory "/usr/local/var/postgres"? 

Now when I look at my Activity Monitor I can see 6 instances of postgress.

How do I fix this?

8 Answers

Public service announcement: never delete postmaster.pid. Really. Great way to get data corruption.

You already had PostgreSQL installed, and you deleted the data dir without stopping the running server. So you now have some orphan PostgreSQL server processes that are managing data files that've been deleted, so they're no longer accessible in the file system and will be fully deleted when the last open file handle to them is closed. You can't use pg_ctl to shut the server down like normal because you've deleted the cluster datadir, so you must simply kill the processes. Kill the postmaster (do not use kill -9, just an ordinary kill will do) and the rest will shut down too.

You will then be able to start a new server in the datadir against the freshly initdb'd data.

It is highly likely that you will experience conflicts down the track unless you uninstall the other older version of PostgreSQL.

In a nutshell:

cat /usr/local/var/postgres/postmaster.pid

Note down the number on the first line, which is the pid of the postmaster.

Verify with ps that the pid is that of a postgres postmaster.

Kill the postmaster process with the following command, replacing 'PID' with the number you have noted down. Again, do not use kill -9 or kill -KILL, just use a plain kill, i.e. a SIGTERM:

kill PID

If the pid is not that of a postgres postmaster, manually kill any postgres backends that may still be running, verify that they are no longer running, and only then remove postmaster.pid. (You must also verify that the postmaster.pid is not on shared storage where the server could be running on some other VM/host).

Another possibility is that you had a hard shutdown and the postgres process died without cleaning up its pid file. This happens to me when my laptop's battery dies.

This solution is not for a production system, and you should really make sure the postgres daemon is not running, but I use my laptop for coding and I'm not worried about needing to regenerate my databases.

So if another process -- or none at all -- is running on that port, just delete the pid file, e.g.

rm /usr/local/var/postgres/postmaster.pid 

and postgres will soon start up fine.

To find out if another process is running on that port, you can do

ps wax | grep `head -1 /usr/local/var/postgres/postmaster.pid` 

Then run

tail -f /usr/local/var/postgres/server.log 

to see if it worked. You should see

FATAL: lock file "postmaster.pid" already exists HINT: Is another postmaster (PID 933) running in data directory "/usr/local/var/postgres"? FATAL: lock file "postmaster.pid" already exists HINT: Is another postmaster (PID 933) running in data directory "/usr/local/var/postgres"? LOG: database system was interrupted; last known up at 2014-05-25 09:41:32 PDT LOG: database system was not properly shut down; automatic recovery in progress 

(or at least that's what I just saw after I did the above :-) )

(And really, shouldn't Postgres be smart enough to realize that there is no process with PID 933 and remove the bogus pid file on its own?)

I tried all of this to no avail after upgrading to Yosemite broke my postgres (installed via homebrew).

Then I stumbled on this blog post:

First I needed to create the missing directories that were apparently wiped out during the upgrade (thanks Apple!).

$ cd /usr/local/var/postgres $ mkdir {pg_tblspc,pg_twophase,pg_stat_tmp} 

Then just start postgres again using the normal homebrew launch sequence:

$ launchctl unload ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist $ launchctl load ~/Library/LaunchAgents/homebrew.mxcl.postgresql.plist 

Thanks Ruckus Notes for helping solve my problem. Hopefully it helps you as well.

HARD REBOOT INSTRUCTIONS

I had this same issue after a hard reboot. After checking the postmaster.pid file's pid, I noticed I had no process running. I didn't want to hard delete the .pid file, instead I used a pg-stop alias I had created in my .bash_profile. this alias just runs

pg_ctl -D /usr/local/var/postgres stop -s -m fast

For Reference

# psql alias pg-start='pg_ctl -D /usr/local/var/postgres -l /usr/local/var/postgres/server.log start' alias pg-stop='pg_ctl -D /usr/local/var/postgres stop -s -m fast' 

log output after pg-stop

LOG: database system was interrupted; last known up at 2016-04-25 10:51:08 PDT LOG: database system was not properly shut down; automatic recovery in progress LOG: record with zero length at 0/274FA10 LOG: redo is not required LOG: database system is ready to accept connections LOG: autovacuum launcher started LOG: received smart shutdown request LOG: autovacuum launcher shutting down LOG: shutting down LOG: database system is shut down LOG: database system was shut down at 2016-04-25 13:11:04 PDT 

brew

I thought I should also mention here that if you have installed postgres with homebrew you should give brew services a look. That is now how I prefer to start/stop my databases.

XXXXX:~ chris$ brew services list Name Status User Plist mongodb stopped postgresql started chris /Users/chris/Library/LaunchAgents/homebrew.mxcl.postgresql.plist redis started chris /Users/chris/Library/LaunchAgents/homebrew.mxcl.redis.plist 

Deleting postmaster.pid is actually a really decent thing to do at every boot, blindly. That's what my system does. Because you've just booted up, you know there is no Postgres process running, and if you're recovering from an unclean shutdown, this file will be there preventing your recovery.

A better design for Postgres would be to put the postmaster.pid file in the /run filesystem, so it is guaranteed to get deleted at every reboot. Many other servers work that way.

I received this error after, I think, my computer crashed. PostgreSQL couldn't even start because of this error so killing the process wasn't the solution. I simply backed-up and then deleted the postmaster.pid file and then the error stopped and PG was able to start again.

Sometimes the humble pg_ctl -w restart can do the trick :-)

I fixed this by doing brew services stop postgresql -- I was doing this on Mac.

I could then start as usual, using either homebrew or manually.

My guess is that pg_ctl -D /usr/local/var/postgres and brew services start create different record files, and you need to start the same way you start.

Good luck.