FATAL ERROR lock file "postmaster.pid" already exists - postgresql

Question

I have recently installed PostGIS on my Mac (El Capitan 10.11.4, Postgres is version 9.5.1) using Homebrew, and I am following these instructions - http://morphocode.com/how-to-install-postgis-on-mac-os-x/
When I try to start Postgres using
pg_ctl -D /usr/local/var/postgres start
I get the following error:
$ FATAL: lock file "postmaster.pid" already exists
HINT: Is another postmaster (PID 280) running in data directory "/usr/local/var/postgres"?
So I spent a few hours researching how to address this, but to no avail.
Notably, I tried to kill the PID as recommended in an answer on Superuser - https://superuser.com/questions/553045/fatal-lock-file-postmaster-pid-already-exists- (in the case above, I ran kill 208), but as soon as I tried to start Postgres again, I got the same error, albeit with a different PID number. I saw a few people recommended deleting the postmaster.pid file, but I feel like maybe I should save that as a last resort...
Admittedly part of the reason I'm not sure how to fix this is that I'm not really clear on what the postmaster even is - I'm just starting to learn about all of this.
Hopping into a Postgres database via the psql db_name command works just fine, for what it's worth.

Answer 1

Posting this in case it helps someone else:
I was having this same problem as the OP after a hard reboot when my laptop crashed. What helped me was running the following command to see what PID was associated with postmaster.pid:
cat /usr/local/var/postgres/postmaster.pid
The first number that appears will be the PID. Looking in Activity Monitor, I was able to see that Postgres was running, but without a PID number that matched the one shown.
Instead of the steps outlined in the answer referenced on Superuser, I restarted my laptop properly and then opened up Terminal and ran
brew services restart postgresql
This worked without having to remove postmaster.pid, which I saw a few other posts recommend. Sometimes it's the simple solutions that work.

Answer 2

I add here what worked for me, after a long time of searching:
Delete the postmaster.pid file:
rm /usr/local/var/postgres/postmaster.pid
Restart your postgres:
brew services restart postgresql
Hope this helps someone ...
Update 8/2022:
As Mike commented, for M1 Mac you would replace stage 1 with:
rm /opt/homebrew/var/postgresql/postmaster.pid
With M1 and specify Postgres Version # 14
rm -rf /opt/homebrew/var/postgresql#14/postmaster.pid

Answer 3

It often happens to me in OSx, when my system shutdown unexpectedly.
You can just remove the file postmaster.pid.
cd Library/Application Support/Postgres/var-{postgres-version}
and remove the postmaster.pid file
in case you use brew then your path should be something like:
/usr/local/var/postgres/postmaster.pid
restart the Postgres by using this command
pg_ctl -D /usr/local/var/postgres restart

Answer 4

Since you can connect to the database, you don't need to start the server again - it's already running.
pg_ctl is used to control the PostgreSQL server. Since your server is already started, your command:
pg_ctl -D /usr/local/var/postgres start
Returns an error, saying that there is a lock on postmaster.pid - which is true since there is already a server running under that PID.
There are two ways:
The most basic way - skip that step, your server is already running!
Executing a needless operation - stopping the server, and then starting it again.
You could stop your server doing :
pg_ctl -D /usr/local/var/postgres stop
So that you won't have the lock on postmaster anymore and you could use your command to start it again.

Answer 5

Postmaster is the main PostgreSQL process. You're trying to start PostgreSQL that's already running (and you're saying yourself you can connect to it). Just skip that step of your process.

Answer 6

When the system shutdown unexpectedly, my postgres crashs and i'm unable to connect to it.
What worked for me was:
1˚ Check postgres log:
tail -n 10000 /usr/local/var/log/postgres.log
2˚ Find the PID of postgress, should look like this:
FATAL: lock file "postmaster.pid" already exists
HINT: Is another postmaster (PID 707) running in data directory "/usr/local/var/postgres"?
3˚ Kill that process:
kill 707
4˚ Restart your postgres
brew services restart postgresql
After those steps i was able to connect to the database within my rails application.

Answer 7

If you got no important data to lose :
sudo killAll postgres
brew services restart postgresql
AGAIN : You could get data corrupted by doing this !
do it at your own risk !

Answer 8

I am using mac and these step work for me:-
step1: cd Library/Application\ Support/Postgres
(most commonly your Postgres installation will be located here)
step2: cd var-13
(if you are using version 12 then use cd var-12. Hope got the point)
step3: ls
(As you can see among the files you find the postmaster.pid, perfect.)
step4: rm postmaster.pid
When you have removed the stale postmaster.pid file you can restart PostgreSQL and everything should work as normal.

Answer 9

My OSX laptop had shutdown unexpectedly, and I was getting a stale postmaster.pid error in the PostgresApp. Shutting down my laptop and turning it back on again solved the problem.

Answer 10

After running the following commands
rm /usr/local/var/postgres/postmaster.pid
brew services restart postgresql
The error lock file "postmaster.pid" already exists comes up again.
When we run launchctl list | grep postgres
28618 0 homebrew.mxcl.postgresql
The existing file "postmaster.pid" was created by this daemon process hosted by launchctl.
We try to stop the homebrew.mxcl.postgresql through
sudo launchctl stop homebrew.mxcl.postgresql
launchctl disable homebrew.mxcl.postgresql
Unfortunately, none of them could stop the homebrew.mxcl.postgresql.
The reason is Disable and enable an agent using (persists between boots)
https://apple.stackexchange.com/questions/105892/disable-services-in-osx-services-msc
launchctl enable <name> or launchctl disable <name>
Two ways to solve it when the error lock file "postmaster.pid" already exists comes up again
In order to stop an agent immediately through
launchctl kill homebrew.mxcl.postgresql
Restart your desktop and run brew services start postgresql#14. Now, PostgreSQL could start successfully.
Hope it could help someone who met the same issue again.

Answer 11

This worked for me. First locate postmaster.pid (for me it was in the var directory as seen below, although it will be different on depending on your operating system). Then get rid of postmaster.pid, then kill the postgres process, then start/restart postgres service.
cd /var/lib/pgsql/data/
rm postmaster.pid
sudo pkill -u postgres
sudo systemctl start postgresql.service

Answer 12

If you have installed postgres with brew then simply run the following command and it will manage everything
brew services restart postgresql