Andrew Beaton :: FAQ

Postfix Mail Queue Commands

Andrew — Wed, 10 Mar 2010 21:03:58 +0000

To resend the mails in the mail queue, type either of the following two commands:

# postfix flush

# postfix -f

To see the mail queue, type:

# mailq

To remove all mail from the mail queue, type:

# postsuper -d ALL

To remove all mails in the deferred mail queue, type:

# postsuper -d ALL deferred

Convert VMware Server 2.0.x VMs into VMware Server 1.0.x

Andrew — Thu, 04 Mar 2010 18:16:37 +0000

If you have ever created a virtual machine using VMware server 2.0 and tried to use them on the previous VMware server 1.0.x you would find the virtual machine would not run and you would be confronted with an error.

The following two steps can be used to fix this and let you run the later virtual machine in the old server.

Open the [VirtualMachine].vmx and change VirtualHw.version to “4″.
Open the [VirtualMachine].vmdk and change ddb.virtualHWVersion to “4″.

Now you will be able to start up the virtual machine as if it were created using the 1.0.x version.

Run a cron job every x seconds

Andrew — Tue, 26 Jan 2010 19:38:57 +0000

As most of you know, the smallest time a cron job can be configured to run is every minute.
To run a script every 15 seconds for example, you could use the following:

main cron job:

* * * * * /path/to/wrapper.sh

wrapper.sh:

/path/to/script &
sleep 15
/path/to/script &
sleep 15
/path/to/script &
sleep 15
/path/to/script &

If you can suggest any nicer alternatives to this example, please let me know.

Can’t create table – errno: 13

Andrew — Wed, 30 Dec 2009 16:19:22 +0000

I came across a problem today when trying to create a temporary table in MySQL.

ERROR 1005 (HY000): Can't create table 'temptable' (errno: 13)

The first thing I checked was that the user in question had the Create_tmp_table_priv privilege in the users table, which it did.

The next step was to find out where MySQL was writing the temporary tables.

The following command tells us this:

show variables like '%dir';
+---------------------------+----------------------------+
| Variable_name             | Value                      |
+---------------------------+----------------------------+
| basedir                   | /usr/                      |
| bdb_logdir                |                            |
| bdb_tmpdir                | /tmp/                      |
| character_sets_dir        | /usr/share/mysql/charsets/ |
| datadir                   | /var/lib/mysql/            |
| innodb_data_home_dir      |                            |
| innodb_log_arch_dir       |                            |
| innodb_log_group_home_dir | ./                         |
| slave_load_tmpdir         | /tmp/                      |
| tmpdir                    | /tmp/                      |
+---------------------------+----------------------------+

And from that we see the tmpdir is located in /tmp/.

A quick checked revealed that MySQL could not create files in this directory, no write access, so a simple permissions change and all was well again.

RPM scriptlet failed

Andrew — Thu, 17 Dec 2009 17:16:48 +0000

I came across a problem when trying to remove an RPM using `rpm -e` which caused this following error to come up.

# rpm -e PACKAGE 
find: ....... No such file or directory
error: %preun(PACKAGE) scriptlet failed, exit status 1

To fix this, I added `—noscripts` to the end of the line and it removed without a problem.

Read MP3 ID3 Tags in Perl

Andrew — Thu, 03 Dec 2009 20:59:12 +0000

The package I use for simple tag reading is MP3::Tag, available on CPAN with more information here.

The following example shows how easy it is to retrieve tags from an MP3 file.

use MP3::Tag;
 
my $file = MP3::Tag->new($filename);
 
my ($title, $track, $artist, $album, $comment, $year, $genre) = $file->autoinfo();
 
print "Title: [$title]\n";
print "Artist: [$artist]\n";
print "Album: [$album]\n";
print "Track: [$track]\n";
print "Year: [$year]\n";
print "Genre: [$genre]\n";
print "Comment: [$comment]\n\n";

SCP files with spaces in them

Andrew — Fri, 27 Nov 2009 20:17:15 +0000

Right, I’m sure we’ve all come across this probem before. You try use SCP to copy a file but it has spaces in the filename or directory name. Well obviously one solution is not to use spaces in filenames or directory names! But some of you lot do, so, try the following:

scp user@host:"'filename with spaces'" destination

Yes, that’s with more quotes!

" + ' + filename with spaces + ' + "

Recursively remove all .svn directories

Andrew — Fri, 27 Nov 2009 20:13:42 +0000

Sometimes you need to clear out all of the .svn files and directories.

The following command will recursively remove each one of them for you:

rm -rf `find . -name .svn`

Backup a MySQL database

Andrew — Fri, 27 Nov 2009 20:10:24 +0000

I’ll just quickly cover some options here to backup a MySQL database.

The first will output all the data and all the databases along with the schema:

mysqldump -u <user> -p -h <hostname> --all-databases > all_databases.sql

The next option will output just the schema for all of the databases:

mysqldump -d -u <user> -p -h <hostname> --all-databases > all_databases.sql

Now we can use the same two methods above but replace –all-databases with the name of a database to output just one.

Redirect root mail to an external e-mail address

Andrew — Fri, 27 Nov 2009 20:04:57 +0000

Add this line to the bottom of /etc/aliases:

root: your_email@domain.com

Run this command:

newaliases

Restart your mail server and run the following command to test:

echo Test | mail -s "Test Message" root