Tag Archives: file system
Private yum repository with Amazon S3

While a public yum repository is easy to set up with S3, going private is more difficult. The privacy must be enforced by some plugin that can retrieve files from the S3 bucket with the API using stored credentials (maybe). Storing credentials can be avoided on EC2 machines that are assigned a proper role, but this is not possible in any other scenario.

Nevertheless, the first steps are common for both public and private setups:

1. Create the proper directory structure

This is achievable with the “createrepo” binary that can be installed on both RedHat and Debian-based systems (e.g. Fedora/Centos or Ubuntu). Running this program results in a “repodata” sub-directory being created with a couple of files that store parsed rpm information.

2. Sync the local repository with the S3 bucket

Continue Reading →

XFS corruption – repairing

Note: The “magical” tool for XFS is (obviously) xfs_repair. Having it running can sometimes be the tough issue.

Introduction

How could a filesystem corruption happen? There are a couple of likely causes to it:

  • Kernel bugs: they are infrequent but they also did happen many times in the past and will still happen in the future. Not many things to be done about them, other than applying patches / keeping the kernel up to date;

  • Memory issues, e.g. memory errors propagated to the file system in control structures: they are usually mitigated with ECC memory but they can never be ruled out;

  • Underlying storage issues: quite unlikely but nevertheless possible;

  • Using the reset button on running servers: journaling file systems are almost always able to recover from such incident;

  • RAID controller issues: this could be the leading cause and not be easy to mitigate, even if firmware upgrade is sometimes possible.

Continue Reading →

The “Debugging” interview – a few pointers

The long interview day is nearing its end. Googamazbook got the best and the worst out of you (well, neither of those, but I’m trying to put some literature in here); the last interviewer comes in, smiles condescendently and greets you with:

Time for the easy interview, heh?

Yes, you have all the reasons to be concerned and feel you’re just one step away from failure (yes, why didn’t you spend the day by the pool in the basement of the many stars hotel they got you a room in for the interview?). But without further ado, the questions start pouring in:

Question 1

How do you figure out if a process is CPU bound or I/O bound?

Tricky! Let’s not jump to the conclusion. There are 2 variables here, this means we have 4 possibilities:

Continue Reading →

Next Page