---
title: Creating PostgreSQL cluster in portable hard drive
date: 2016-10-18 21:14:55.547276 UTC
---
I'm working as a part-time software developer for [EasyUni](http://www.easyuni.com). Its database is so huge that I cannot install on my laptop's internal HDD. I have to look for a way to install it in my portable HDD.

My solution is to create a second PostgreSQL cluster with data directory residing in my portable HDD. This cluster must not be started up automatically, because the portable HDD is not always attached. So my command to create this second cluster is:

```
sudo pg_createcluster 9.5 second -d /media/quan/Quan-Backup/Postgres/second --start-conf=manual
```
given that:

- 9.5 is the version of PostgreSQL
- `second` is the name of this cluster
- _/media/quan/Quan-Backup/_ is the mount point of my portable HDD. This mount point is created automatically by [GNOME](https://www.gnome.org/) after I plug the HDD in and authenticated for decryption (my HDD is encrypted with [LUKS](https://en.wikipedia.org/wiki/Linux_Unified_Key_Setup)).
- `--start-conf=manual`: This cluster has to be started manually.

The first time doing, the command failed:

```
Creating new cluster 9.5/second ...
  config /etc/postgresql/9.5/second
  data   /media/quan/Quan-Backup/Postgres/second
  locale en_US.UTF-8
initdb: could not access directory "/media/quan/Quan-Backup/Postgres/second": Permission denied
Error: initdb failed
```

It is mythical because the folder _/media/quan/Quan-Backup/Postgres/second_ was actually created and set with proper owner & permission!

Following [one guy](http://dba.stackexchange.com/a/62037) in StackExchange, I tested if user _postgres_ is able to access the folder:

```
$ sudo -u postgres ls /media/quan/Quan-Backup/Postgres/second 
ls: cannot access '/media/quan/Quan-Backup/Postgres/second': Permission denied
```

Funny, because:
```
$ ll /media/quan/Quan-Backup/Postgres 
total 4.0K
drwxr-xr-x 2 postgres postgres 4.0K Oct 19 10:29 second
```
It had the `x` flag as suggested by [another guy](http://dba.stackexchange.com/a/150970).

But, combining the two hints, I suspected that the `x` flags of parents folder also affect. So I checked:

```
$ ll /media                                                          
total 4.0K
drwxr-x---+ 3 root root 4.0K Oct 19 09:29 quan
```
_/media/quan_ didn't have `x` flag for _other_ user. I fixed it and tried creating Postgres cluster again:

```
$ sudo chmod a+x /media/quan
$ sudo pg_createcluster 9.5 second -d /media/quan/Quan-Backup/Postgres/second --start-conf=manual
Creating new cluster 9.5/second ...
  config /etc/postgresql/9.5/second
  data   /media/quan/Quan-Backup/Postgres/second
  locale en_US.UTF-8
  socket /var/run/postgresql
  port   5433
```

Hooray! It works.

From that on, everytime I want to use that cluster, I need to run it with:

```
sudo pg_ctlcluster 9.5 second start
```