Krdytkyu

[Ubuntu 16.04]
I installed postgresql 9.5 along with dependencies:

sudo sh -c "echo 'deb http://apt.postgresql.org/pub/repos/apt/ xenial-pgdg main' > /etc/apt/sources.list.d/pgdg.list"

wget --quiet -O - http://apt.postgresql.org/pub/repos/apt/ACCC4CF8.asc | sudo apt-key add -

sudo apt-get update

sudo apt-get install postgresql-common

sudo apt-get install postgresql-9.5 libpq-dev

When I want to run psql then I get:

psql: could not connect to server: No such file or directory

    Is the server running locally and accepting

    connections on Unix domain socket "/var/run/postgresql/.s.PGSQL.5432"?

But /var/run/postgresql/ is empty. When I restart posgresql everything appears to be fine:

$ /etc/init.d/postgresql restart

[ ok ] Restarting postgresql (via systemctl): postgresql.service.



$ /etc/init.d/postgresql status

● postgresql.service - PostgreSQL RDBMS

   Loaded: loaded (/lib/systemd/system/postgresql.service; enabled; vendor preset: enabled)

   Active: active (exited) since wto 2016-09-27 16:18:26 CEST; 1min 15s ago

  Process: 3076 ExecReload=/bin/true (code=exited, status=0/SUCCESS)

  Process: 3523 ExecStart=/bin/true (code=exited, status=0/SUCCESS)

 Main PID: 3523 (code=exited, status=0/SUCCESS)

but if check ps aux there is not such PID (why??)

Total reinstalation doesn't help at all. How can I fix it?

This is an idiosyncrasy of the systemd integration of PostgreSQL in Xenial.

The postgresql service unit installed by the postgresql-common package is just a dummy service which causes the actual service postgresql@9.6-main to be started via a dependency. You can see that dependency by running the command

systemctl list-dependencies postgresql

That dependency is not permanent, but generated during system boot by the systemd generator /lib/systemd/system-generators/postgresql-generator which also comes with the postgresql-common package. The generator checks whether the startup mode in the file /etc/postgresql/9.6/main/start.conf is set to auto, and if so, sets up the dependency that subsequently causes instance 9.6-main to be started.

(More precisely, it checks all configuration subdirectories /etc/postgresql/*/* and will create dependencies for all instances that are configured for automatic startup, but in a default installation there will be just the one instance.)

Due to the limitations of systemd generators (see man systemd.generator) this process may fail, causing the dependencies to be absent after a reboot.
Systemd will then start only the dummy service, writing

systemd[1]: Starting PostgreSQL RDBMS...

systemd[1]: Started PostgreSQL RDBMS.

to the log but otherwise doing nothing.
Attempting to start the service manually by

systemctl start postgresql

will just reproduce that result.
Running the command

systemctl daemon-reload

manually as root will re-run the generator and in most cases fix the problem until the next reboot.

To solve the problem permanently you'll have to find the reason why the generator fails during boot. Possible causes can be found in the systemd.generator manpage. In my case it was the PostgreSQL config file /etc/postgresql/9.6/main/postgresql.conf which was symlinked to a different filesystem that wasn't available yet when the generator ran early during boot. postgresql-generator checks the existence of that file even though it doesn't otherwise need it.

Extending on the answer of Tilman, but not enough Kudos to comment...

If you do not need the service to be called postgresql and do not care about the wrapper dummy service, it should work to just to control the real service directly. It's name is : postgresql@$version-$cluster.service In your case it should be postgresql-9.5-main in short. Like to start

systemctl start postgresql@9.5-main

and to stop:

systemctl stop postgresql@9.5-main

Status will also give you much better and accurate information than on the auto generated wrapper service.

systemctl status postgresql@9.5-main

For 9.6 it looks like this:

● postgresql@9.6-main.service - PostgreSQL Cluster 9.6-main

   Loaded: loaded (/lib/systemd/system/postgresql@.service; disabled; vendor preset: enabled)

   Active: active (running) since Wed 2017-09-13 00:41:50 CEST; 7h ago

  Process: 10235 ExecStop=/usr/bin/pg_ctlcluster --skip-systemctl-redirect -m fast %i stop (code=exited, status=2)

  Process: 10676 ExecStart=postgresql@%i --skip-systemctl-redirect %i start (code=exited, status=0/SUCCESS)

 Main PID: 10683 (postgres)

   CGroup: /system.slice/system-postgresql.slice/postgresql@9.6-main.service

           ├─10683 /usr/lib/postgresql/9.6/bin/postgres -D /var/lib/postgresql/9.6/main -c config_file=/etc/postgresql/9.6/main/postgresql.conf

           ├─10685 postgres: 9.6/main: checkpointer process

           ├─10686 postgres: 9.6/main: writer process

           ├─10748 postgres: 9.6/main: wal writer process

           ├─10749 postgres: 9.6/main: autovacuum launcher process

           ├─10750 postgres: 9.6/main: archiver process   last was 000000020000000000000082

           ├─10751 postgres: 9.6/main: stats collector process

In my case this was related to incorrectly configured locales.

I've found the solution in this dba.stackexchange.com answer:

1. Use sudo dpkg-reconfigure locales to generate the necessary locales


2. Drop the existing database cluster via sudo pg_dropcluster 9.5 main (this will erase all the data in the cluster!)


3. Re-create the cluster via sudo pg_createcluster 9.5 main --start
   


4. Restart PostgreSQL via sudo service postgresql restart
   

it would better to use systemd startup scripts with ubuntu 16.04 , init scripts might not work properly these days. Postgres 9.5 is already in the ubuntu repos so try that instead , it should have systemd startup.

Another "got bitten by this".

The pg_upgradecluster actually left the target version (9.6) in "manual" mode on port 5433 and source version (9.5) at port 5432.

Even after pg_dropcluster 9.5. Editing the start.conf file didn't help, but the hint was to use systemctl daemon-reload, since the generator decides based on this configuration file whether to symlink the service file:

for conf in /etc/postgresql/*/*/postgresql.conf; do

    # trimmed for brevity

    [ "$start" = "auto" ] || continue

    ln -s "$pgservice" "$wantdir/postgresql@$version-$cluster.service"

done

So if the cluster you want started does not have the word "auto" in start.conf, you need to do a system-reload (or reboot) to have it enabled at boot time.

Still have to verify this with a reboot, but given the above pretty confident that was the issue.

I disabled the magic "super service" like this:

root@server# systemctl disable postgresql

Then I activated the concrete service:

root@server:~# systemctl enable postgresql@9.5-main.service 

After rebooting everything worked again.

Had the same error, wasted hours, simple solution. Check this SO question and my answer, Which is:

sudo service postgresql restart