wpkg --database-is-locked

Submitted by Alexis Wilke on Thu, 11/01/2012 - 06:45
Options Comments
--admindir Define the administration directory, where the database of the installed packages resides.
--debug Define a set of flags of things to print out for debug purposes.
--instdir Define the installation directory, where the data files are installed on the target.
--quiet Request for warning messages to not be displayed.
--root Define the installation root path.
--verbose Display log information of level INFO.

wpkg makes use of a database which cannot be shared between multiple processes. To avoid problems (when running two wpkg processes in parallel) the tool creates a lock file in its database.

The --database-is-locked command is used to check whether that lock file exists. If it does exist it means a wpkg process is running.

Note that it is possible to do work on the wpkg database with other tools or scripts using the --create-database-lock and the --remove-database-lock commands and then make sure that you don't walk on your own feet (i.e. prevent two instances of that other tool to manipulate the database simultaneously) using the --database-is-locked test.

The following is a very basic example of a shell script using these commands, note that this example doesn't handle the case where the user would use Ctrl-C to break execution (because in that case you probably want to make sure the database is in a clean state and then --remove-database-lock is used.)

#!/bin/sh
if wpkg --database-is-locked
then
  echo "error: Sorry! The wpkg database is currently in use. Try again later."
  exit 1;
fi
if ! wpkg --create-database-lock
then
  echo "error: Sorry! The wpkg database could not be locked properly."
  exit 1;
fi
[... DO YOUR WORK ...]
wpkg --remove-database-lock

The reason why the --create-database-lock may fail is because another process may lock the database between the time we check with --database-is-locked and the time we create the lock with --create-database-lock.