I am relatively new to postgres and at first I was backing up and restoring databases using pgadmin4. I was just using postgres user because this is the default one that you get to use when working with pgadmin. After developing a web project using postgres, I needed to move the database I used to somewhere else. This time, I needed to restore the backup using CLI instead of the GUI pgadmin that I was used to.
The backup sql created in pgadmin is created using custom format, which I found it hard to restore through cli commands. It failed when used with pg_restore for many reasons. Most of the errors that I faced was due to permissions.
Here I introduce how I created a backup of a database and restored it through cli. Other ways are possible, so just use this as a reference.
Creating backup
For this example, I am going to backup a database named test. I am going to backup using postgres user account, which is a superuser itself. I tried backup with a created user, but it failed, so just to make things simple, I am going to backup with postgres account to avoid any permission issues.
I am using postgres server v13.
first change terminal user to postgres
$ su postgres
run pg_dump command
$ pg_dump -d test -f dump.sql
Here I did not specify user since I am already postgres user. I am telling it to backup database named test, and save the dump to file named dump.sql.
Since postgres is the superuser in postgres server, this command will dump a database with least problems. This command will save sql in plain text by default.
Restoring backup
Once this dump file has been move to a target machine, again change terminal user to postgres.
$ su postgres
use pg_restore to restore the database to target machine’s postgres server.
$ pg_restore -d test < dump.sql
this command is telling to restore database named test from backup file dump.sql. In the dump creating command used above, it doesn’t include a sql command to create the database. Therefore, this restoring command required that a database named test already exists in the target machine’s postgres server. If not, then the user should create one after logging into psql.
For convenience, if the user want the dump file to include a database creating sql command, then the dump creating command should have -x option, so it should look like this:
$ pg_dump -d test -x -f dump.sql
Instead of using pg_dump command, one can use psql to restore from plain sql file. The following command will read the sql commands as written with specified postgres user and database. This command also works in windows.
$ psql -U user -d dbname -f dump.sql
Why change user to postgres before executing pg_dump, pg_restore?
postgres did not allow password authenticated login. It was set to peer authentication, which means that I can only login to postgres using psql command as postgres user only if I am postgres user in terminal. If I try to login as postgres user with password, it did not work. Of course, I found a workaround to force postgres server to allow postgres user authentication by password, but for some reason it did not work for me. Thus, the only option that I had was to change terminal user to postgres and then access postgres server.
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