Databases, Systems & Networks

there’s always apt-cache policy <package-name> (no sudo needed).

Not installed:

olivier@neews:/$ apt-cache policy gnuift
 gnuift:
   Installed: (none)
   Candidate: 0.1.14-11
   Version table:
      0.1.14-11 0
         500 http://archive.ubuntu.com/ubuntu/ oneiric/universe amd64 Packages

Installed:

olivier@neews:/$ apt-cache policy firefox
 firefox:
   Installed: 8.0+build1-0ubuntu0.11.10.3
   Candidate: 8.0+build1-0ubuntu0.11.10.3
   Version table:
  *** 8.0+build1-0ubuntu0.11.10.3 0
         500 http://archive.ubuntu.com/ubuntu/ oneiric-updates/main amd64 Packages
         500 http://archive.ubuntu.com/ubuntu/ oneiric-security/main amd64 Packages
         100 /var/lib/dpkg/status
      7.0.1+build1+nobinonly-0ubuntu2 0
         500 http://archive.ubuntu.com/ubuntu/ oneiric/main amd64 Packages

Or dpkg: dpkg -l | grep -E '^ii' | grep <package name>. When it’s not installed it won’t show output. When it is, it’ll show something like:

olivier@neews:~$ dpkg -l | grep -E '^ii' | grep firefox
 ii  firefox                                                     8.0+build1-0ubuntu0.11.10.3                            Safe and easy web browser from Mozilla
 ii  firefox-branding                                            8.0+build1-0ubuntu0.11.10.3                            Safe and easy web browser from Mozilla - transitional package
 ii  firefox-globalmenu                                          8.0+build1-0ubuntu0.11.10.3                            Unity appmenu integration for Firefox
 ii  firefox-gnome-support                                       8.0+build1-0ubuntu0.11.10.3                            Safe and easy web browser from Mozilla - GNOME support
 ii  firefox-locale-en                                           8.0+build1-0ubuntu0.11.10.3                            English language pack for Firefox

It's obviously a fuzzier search but handy if you're not sure which package you're looking for.
 
 For manually installed things...
 
 A bit harder but if they're on the current path, you could just run them. That's a bit of mission so I'd rather just run:
 
 oli@bert:/$ which chromium-browser
 /usr/bin/chromium-browser

And:

oli@bert:/$ which gnuift
# returns nothing

Which is better?

That depends on the sanity of user. There’s nothing to stop somebody installing something called chromium-browser that isn’t Chromium. They could even package it up incorrectly and install that. Neither method can be 100% certain.

But assuming the owner is sane – packages should be good enough for most people.

To clone a Debian installation, use the apt-clone utility. It’s available (as a separate package, not part of the default installation) in Debian since wheezy and in Ubuntu since 12.04. On the existing machine, run

apt-clone clone foo

This creates a file foo.apt-clone.tar.gz. Copy it to the destination machine, and run

apt-get install apt-clone
apt-clone restore foo.apt-clone.tar.gz

If you’re working with an old system where apt-clone isn’t available, or if you just want to replicate the list of installed packages but not any configuration file, here are the manual steps.

• On the source machine:

cat /etc/apt/sources.list /etc/apt/sources.list.d >sources.list
pkg --get-selections >selections.list
apt-mark auto >auto.list

• On the target machine:

cp sources.list /etc/apt/
apt-get update
/usr/lib/dpkg/methods/apt/update /var/lib/dpkg/
dpkg --set-selections <selections.list
apt-get dselect-upgrade
xargs apt-mark auto <auto.list

I believe that you’re affected by an incompatible change in dpkg that first made it into wheezy. See bug #703092 for background.

The short story is that dpkg --set-selections now only accepts package names that are present in the file /var/lib/dpkg/status or /var/lib/dpkg/available. If you only use APT to manage packages, like most people, then /var/lib/dpkg/available is not kept up-to-date.

After running apt-get update and before running dpkg --set-selections and apt-get -u dselect-upgrade, run the following command:

apt-cache dumpavail >/tmp/apt.avail
dpkg --merge-avail /tmp/apt.avail

From jessie onwards, you can simplify this to

apt-cache dumpavail | dpkg --merge-avail

Alternatively, run

/usr/lib/dpkg/methods/apt/update /var/lib/dpkg/

or even simpler

apt-get install dctrl-tools
sync-available

Another simple method that doesn’t require installing an additional package but will download the package lists again is

dselect update

See the dpkg FAQ for more information. (This is mentioned in the dpkg man page, but more in a way that would remind you of the issue if you were already aware, not in a way that explains how to solve the problem!)

Note that cloning a package installation with dpkg --set-selections doesn’t restore the automatic/manual mark in APT. See Restoring all data and dependencies from dpkg –set-selections ‘*’ for more details. You can save the marks on the source system with

apt-mark showauto >auto.list

and restore them on the target system with

xargs apt-mark auto <auto.list

This past weekend, we had a user who was locked out of WordPress Admin panel of their site. While we had written numerous articles covering each specific issue, we realized that we should combine all of them at one place to make it easier for others. In this article, we will show you what to do when you are locked out of WordPress Admin (wp-admin), so you can regain access to your site.

There are few reasons why you could be locked out of WordPress admin, so let’s take a look at each of them one by one. Hopefully through this process of elimination, you will be able to figure out the solution for your problem.

Error Establishing Database Connection

Are you seeing this error on your entire site? The reason why you get this error is because WordPress is unable to establish a database connection. This could happen for various reasons. It could happen if your database got corrupted for some reason. It could happen if your web hosting server is having some issues. If this is your issue, then please refer to our guide on how to fix the error establishing database connection in WordPress.

White Screen of Death

Are you seeing a white screen on your WordPress admin? This issue is often referred to as the WordPress white screen of death. It usually happen because you exhausted the memory limit. It could be caused by a poorly coded plugin or theme. It could also be caused by unreliable web hosting. If you are seeing this error, then please refer to our guide on how to Fix the WordPress white screen of death.

Incorrect Password Issue

Sometimes, even when you are typing the correct username and password combination, you won’t be able to login. When you try to reset your password, you never receive the email. This can happen if you were a victim of a hack. We would recommend that you reset your WordPress password from phpMyAdmin.

This method can be a bit overwhelming for new users, but this is your best bet.

Lost Admin Privileges

Sometimes, you may be able to login to your WordPress admin, but you don’t see any of the admin functionality. For example, no plugins, no themes etc. This could happen if your user permissions were modified. Often this happen due to a hack. Hackers would infect your site, and then delete your admin privileges. In this case, you should add an admin user to the WordPress database via MySQL (phpMyAdmin).

PHP Errors (i.e Syntax error, unexpected function etc)

These PHP errors usually happen when you are pasting the code from a website. Often beginners use the built-in WordPress editor from their dashboard. While that feature is pretty handy, but if you don’t know what you are doing, then it can be a disaster. If you pasted a code from a website which locked you out of your WordPress admin, then the first thing you need to do is take a deep breath. Now the only way to fix this issue is using a FTP program (How to use FTP). Once you have installed the FTP program, login to your site. Go to the theme file that you modified. Most likely it was the functions.php file. Now get rid of the code that you added in there. Re-upload the file, and you should be good to go.

Before you go on the site and comment “this code broke my website”, please refer to our beginner’s guide to pasting snippets from the web into WordPress. This is just to prevent you from looking like a fool on the web. Often its hard to admit that the mistake might be yours, so make sure of that first before you point the finger at someone else.

Hopefully after going through all of these possible scenario’s, you have already fixed your site. If one of these solutions helped fix your issue, then please let us know in the comments. If you have a solution that is not mentioned in this article, then please share it in the comments as well.

Source: wpbeginner.com