Andrew Beaton :: FAQ » Linux

Grep to find ^M (Windows carriage return)

Andrew — Wed, 13 Jul 2011 16:58:17 +0000

There are two options here, one we used before when searching for the ^M’s in VI, the other is new:

^M

$'\r'

So to find all files with the Windows carriage return in them, use one of the following…

grep -r "^M" *

grep -r $'\r' *

^M is entered by pressing Ctrl+V followed by Ctrl+M

List and Install Security Updates via YUM

Andrew — Fri, 08 Jul 2011 17:04:30 +0000

You can now easily find out what security updates there are for your system (RHEL / CentOs / Fedora) by installing the ‘yum-security‘ plugin.

# yum install yum-security

To list available updates and see the relevant advisory code, use the following command:

# yum list security

To obtain information on the returned advisory codes, use the following:

# yum info-security

To list updates that are security relevent, use the following:

# yum --security check-update

And finally, to install only the security update packages, use the following:

# yum update --security

Add a program to start on LXDE startup

Andrew — Fri, 08 Jul 2011 16:33:22 +0000

If you need to get a program to start every time you boot into LXDE, you simply need to add it to the startup file here:

/etc/xdg/lxsession/LXDE/autostart

Add a line at the bottom of the file with the @ symbol and the program to run, for example:

@conky -c ~/.conky/.conkyrc.main &

View output of the dd command

Andrew — Thu, 23 Jun 2011 10:48:36 +0000

Recently whilst wiping some old hard disks I thought it would be useful to see what the ‘dd’ command was doing, rather than sitting there blankly for hour. I knocked up a little bash script to run in another terminal that will update the terminal running dd with some useful status information.

In this example, dd will be run as…

$ dd if=/dev/random of=/dev/sda

copy the following into ddUpdate.sh for example and run it…

#!/bin/sh ddpid=`ps auwx | awk '/dd if/ && !/awk/ { print $2}'` while [ "$ddpid" != "" ] do kill -USR1 $ddpid sleep 1 ddpid=`ps auwx | awk '/dd if/ && !/awk/ { print $2}'` done

This outputs the following to the terminal running dd…

xxxxxx records in xxxxxx records out xxxxxx bytes (xx nn) copied, xxxx s, xx MB/s

Get DateTime in YYYY-mm-dd HH:MM:SS format using Perl

Andrew — Thu, 14 Apr 2011 11:54:34 +0000

For many years I’ve been using the long process of obtaining everything from localtime(), adding 1900 to the year etc. etc. but I’ve just come across the method below, which uses strftime from the POSIX module.

use POSIX; my $DateTime = strftime "%F %T", localtime $^T;

This gives you:

2006-10-02 02:06:07

Now that’s a lot easier!

Remove ^M character with VI

Andrew — Wed, 10 Nov 2010 21:54:36 +0000

To remove ^M’s from a file, type the following:

:%s/[ctrlkey+v and ctrl-key+M]//g

The actual command is:

:%s/^V^M//g

MySQL error /usr/libexec/mysqld: unknown option ‘skip-bdb’

Andrew — Fri, 01 Oct 2010 11:29:00 +0000

MySQL version x is failing to start after upgrade with the following error:

/usr/libexec/mysqld: unknown option ‘—skip-bdb’

To fix comment out the following line in your my.cnf file:

#skip-bdb

You should now be able to restart MySQL

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

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.