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Displaying posts with tag: SELinux (reset)

Connection Failures Between Nodes in MySQL Cluster
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If you're setting up MySQL Cluster on Oracle Linux or another Linux such as Red Hat, CentOS or Fedora, you might have come across some problems getting the nodes to communicate. There are two ways you might bump into problems with network connectivity: The iptables firewall, and SELinux. These security mechanisms might prevent your various nodes—management, data, and API—from communicating with each other in various ways and with various symptoms.

Let's have a look at what you're likely to see. 

Data nodes stuck at "starting"

The first thing you might notice is that your data nodes get stuck in the "starting" state. Running show in the management client gives something like this:

[ndbd(NDB)]     2 node(s)
id=2    @192.168.56.211  (mysql-5.6.11
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SELinux and MySQL
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I've previously written about AppArmor and MySQL, and how to change MySQL's default file locations on systems with AppArmor enabled. Ubuntu and SUSE ship with AppArmor enabled, but some other distributions such as Oracle Linux don't, along with related distrubutions such as Red Hat, CentOS and Fedora. Rather, these other distributions use another mandatory access control system called SELinux. 

Here's some technical detail that might come in handy later.

SELinux uses concepts such as types and domains. Types belong to resources such as files and ports; these are the "objects" in SELinux. Domains contain the "subjects" (processes) and object types that are associated with each other in some

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A difficult XtraBackup restore
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There was one MySQL server with a Adaptec Raid controller and 4 disks. One of the disks was having media errors and caused the whole SCSI bus to become unavailable.

This resulted in a corrupted InnoDB table.

Luckily we did have backups. A full backup and incrementals.

So to restore the backups I installed XtraBackup and MySQL 5.5 on another server.

Then the first step was to 'prepare' the backup. This worked okay for the full backup (redo only).

The second step to add the incremantals failed for the first incremental. This was easily resolved by specifying the full paths instead of relative paths.

Then the backup was fully prepared using the redo logs and undo logs.

As XtraBackup doesn't backup your my.cnf we copied the my.cnf from another server and adjusted it for this server. The my.cnf in your













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Apache Can't Use Remote MySQL Server When SELinux is Enabled
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I don't know why SELinux problems seem so frustrating. The problem almost certainly is related to the fact that there is frequently no error message. This is exactly the problem I ran into while turning up a new Apache web server on Red Hat Enterprise Linux 6 (RHEL6) with SELinux enabled.

The problem is that SELinux prevents Apache from making network connections by default. This is defined by the SELinux boolean httpd_can_network_connect_db. In order to change this value, issue the following

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Linus on Instantiation and Armadaification
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I feel a sense of pride when I think that I was involved in the development and maintenance of what was probably the first piece of software accepted into Debian which then had and still has direct up-stream support from Microsoft. The world is a better place for having Microsoft in it. The first operating system I ever ran on an 08086-based CPU was MS-DOS 2.x. I remember how thrilled I was when we got to see how my friend’s 80286 system ran BBS software that would cause a modem to dial a local system and display the application as if it were running on a local machine. Totally sweet.

When we were living at 6162 NE Middle in the nine-eight 292, we got an 80386 which ran Doom. Yeah, the original one, not the fancy new one with the double barrel shotgun, but it would probably run that one, too.

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The blog was down yesterday
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The brief outage was due to a scheduled move of the servers to a separate rack and subnet dedicated to our work with the Center for Information Assurance & Cybersecurity (ciac) at the University of Washington Bothell (uwb), and a11y.com

I am currently exercising the new (to us) equipment and hope to winnow the less than awesome equipment over the next quarter. I spent the last six months finding the best in breed of the surplussed DL385 and DL380 chassis we (work) were going to have recycled. The team and I were able to find enough equipment to bring up one of each with eight and six gigs of memory, respectively. These will make excellent hypervisors for provisioning embedded instances of Slackware, Fedora, RHEL, CentOS, Debian, FreeBSD, OpenSolaris, OpenIndiana, FreeDOS, etc.

When I initially configured this xen paravirt environment, I failed to plan for integration with libvirt, so I am

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Stop Disabling SELinux!
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I see a lot of people coming by #centos and similar channels asking for help when they’re experiencing a problem with their Linux system. It amazes me how many people describe their problem, and then say something along the lines of, “and I disabled SELinux...”. Most of the time SELinux has nothing to do with the problem, and if SELinux is the cause of the problem, why would you throw out the extra security by disabling it completely rather than configuring it to work with your application?

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MySQL + SELinux: Can't change dir (Errcode: 13)
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If you're using a non-standard MySQL data directory on your Red Hat Enterprise Linux (RHEL) server, you may have seen an error like /usr/libexec/mysqld: Can't change dir to '/mysql_data/' (Errcode: 13). The key to fixing this problem is to ensure the new MySQL data directory has the proper SELinux security context. In my case:

# chcon -R system_u:object_r:mysqld_db_t /mysql_data/

After that, mysqld should start up fine.

Resolving PHP-MySQL Connection Issues
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I ran into an interesting issue when installing Wordpress on my re-installed server, I could not get a database connection during installation. I added some debugging and discovered that I had a "Can't connect to MySQL server on" error returned after the call to mysql_connect() in PHP.

To check the source of the issue I then tried to connect on the command-line using the mysql client, which occurred successfully, confirming that I was using the correct credentials and host address (this was a remote MySQL server).

I next created a test PHP script with a simple mysql_connect() call, and executed it with "php test.php" from the command-line, which was also successful.

Finally I accessed test.php through a browser, where again the connection failed.

So I was dealing with a situation where it was Apache in particular that was unable to connect to the remote

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The unexpected consequences of SELinux
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I’ve been working with a client recently who has SELinux on his servers.  It has been quite a struggle sometimes. My colleages tell me that SELinux has a pretty noticeable performance impact.  I am not sure if we have benchmarks to support this; at any rate, the client said it’s OK, we’ll take the performance hit. There [...]
Showing entries 1 to 10 of 11 1 Older Entries

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