Ubuntu – Can’t install libpq-dev, ubuntu 10.10 and postgres 9

CAUTION The answer about changing the UNIX password for "postgres" through "$ sudo passwd postgres" is not preferred, and can even be DANGEROUS!

This is why: By default, the UNIX account "postgres" is locked, which means it cannot be logged in using a password. If you use "sudo passwd postgres", the account is immediately unlocked. Worse, if you set the password to something weak, like "postgres", then you are exposed to a great security danger. For example, there are a number of bots out there trying the username/password combo "postgres/postgres" to log into your UNIX system.

What you should do is follow Chris James's answer:

sudo -u postgres psql postgres

# \password postgres

Enter new password: 

To explain it a little bit. There are usually two default ways to login to PostgreSQL server:

1. By running the "psql" command as a UNIX user (so-called IDENT/PEER authentication), e.g.: sudo -u postgres psql. Note that sudo -u does NOT unlock the UNIX user.

2. by TCP/IP connection using PostgreSQL's own managed username/password (so-called TCP authentication) (i.e., NOT the UNIX password).

So you never want to set the password for UNIX account "postgres". Leave it locked as it is by default.

Of course things can change if you configure it differently from the default setting. For example, one could sync the PostgreSQL password with UNIX password and only allow local logins. That would be beyond the scope of this question.

• Try apt-get update and then the install.

• Go into aptitude and use the "Cancel pending actions" command in the Actions menu. Then retry the install.

• If that doesn't work, you can always try finding the specific version of the .deb it wants online and install it manually. This looks like where you can download it (make sure to get the i386 version or whatever matches your architecture).

  Once you get the .deb on your local system you can do a dpkg -i libpq-dev_8.4.5-1~bpo50+1_i386.deb and it will install it. But it might complain about missing dependencies, which are listed on that page. You'd have to track down what's missing and install them manually as well.