How do I disable “Command-q” in OS X?

You can reassign menu commands in Mac’s System Preferences menu to different shortcuts, either for individual applications or for all applications. This will let you effectively reassign Cmd-Q to anything (or nothing), if you’d like.

1. Go to System Preferences, and select Keyboard.

2. Click on Keyboard Shortcuts, then select the Application Shortcuts menu bar in the lower left.

3. Click the “+” button to add a shortcut for an application. For this example, we’ll disable Cmd-Q for Google Chrome.

4. Figure out the command name for Google Chrome’s “Quit” by going to the menu bar in Google Chrome and finding the menu item. In Chrome, under the “Chrome” menu bar element, you can find the action “Quit Google Chrome” attached to Cmd-Q.

5. Put the exact name of the menu action item as a new keyboard shortcut in the Keyboard Shortcut options.

6. Select a shortcut that isn’t Cmd-Q (for example, Cmd-Option-Q). Click “Add” to finish the setting.

via How do I disable “Command-q” in OS X? – Quora.

s3ql – a full-featured file system for online data storage

I am really impressed by my first look at s3ql. A really complete, just working and well documented tool to mount aws s3 and other cloud storage solution on a dedicated server:

S3QL is a file system that stores all its data online using storage services like Google Storage, Amazon S3 or OpenStack. S3QL effectively provides a hard disk of dynamic, infinite capacity that can be accessed from any computer with internet access running Linux, FreeBSD or OS-X.

S3QL is a standard conforming, full featured UNIX file system that is conceptually indistinguishable from any local file system. Furthermore, S3QL has additional features like compression, encryption, data de-duplication, immutable trees and snapshotting which make it especially suitable for online backup and archival.

S3QL is designed to favor simplicity and elegance over performance and feature-creep. Care has been taken to make the source code as readable and serviceable as possible. Solid error detection and error handling have been included from the very first line, and S3QL comes with extensive automated test cases for all its components.

Features

  • Transparency. Conceptually, S3QL is indistinguishable from a local file system. For example, it supports hardlinks, symlinks, ACLs and standard unix permissions, extended attributes and file sizes up to 2 TB.
  • Dynamic Size. The size of an S3QL file system grows and shrinks dynamically as required.
  • Compression. Before storage, all data may compressed with the LZMA, bzip2 or deflate (gzip) algorithm.
  • Encryption. After compression (but before upload), all data can AES encrypted with a 256 bit key. An additional SHA256 HMAC checksum is used to protect the data against manipulation.
  • Data De-duplication. If several files have identical contents, the redundant data will be stored only once. This works across all files stored in the file system, and also if only some parts of the files are identical while other parts differ.
  • Immutable Trees. Directory trees can be made immutable, so that their contents can no longer be changed in any way whatsoever. This can be used to ensure that backups can not be modified after they have been made.
  • Copy-on-Write/Snapshotting. S3QL can replicate entire directory trees without using any additional storage space. Only if one of the copies is modified, the part of the data that has been modified will take up additional storage space. This can be used to create intelligent snapshots that preserve the state of a directory at different points in time using a minimum amount of space.
  • High Performance independent of network latency. All operations that do not write or read file contents (like creating directories or moving, renaming, and changing permissions of files and directories) are very fast because they are carried out without any network transactions. S3QL achieves this by saving the entire file and directory structure in a database. This database is locally cached and the remote copy updated asynchronously.
  • Support for low bandwidth connections. S3QL splits file contents into smaller blocks and caches blocks locally. This minimizes both the number of network transactions required for reading and writing data, and the amount of data that has to be transferred when only parts of a file are read or written.

 

http://code.google.com/p/s3ql/

 

NFS cluster status and HighlyAvailableNFS

While working on an NFS cluster setup, I stumbled upon these two articles which are maybe helpful for someone:

http://billharlan.com/pub/papers/NFS_for_clusters.html

Saturated network?

$ time dd if=/dev/zero of=testfile bs=4k count=8182
  8182+0 records in
  8182+0 records out
  real    0m8.829s
  user    0m0.000s
  sys     0m0.160s

 

First exercise your disk with your own code or with a simple write operation like writing files should be enough to test network saturation. When profiling reads instead of writes, call umount and mount to flush caches, or the read will seem instantaneous:

$ cd /
$ umount /mnt/test
$ mount /mnt/test
$ cd /mnt/test
$ dd if=testfile of=/dev/null bs=4k count=8192

Check for failures on a client machine with:

  $ nfsstat -c
or
  $ nfsstat -o rpc

If more than 3% of calls are retransmitted, then there are problems with the network or NFS server. Look for NFS failures on a shared disk server with:

  $ nfsstat -s
or
  $ nfsstat -o rpc

It is not unreasonable to expect 0 badcalls. You should have very few “badcalls” out of the total number of “calls.”

Lost packets

NFS must resend packets that are lost by a busy host. Look for permanently lost packets on the disk server with:

$ head -2 /proc/net/snmp | cut -d' ' -f17
  ReasmFails
  2

If you can see this number increasing during nfs activity, then you are losing packets. You can reduce the number of lost packets on the server by increasing the buffer size for fragmented packets:

$ echo 524288 > /proc/sys/net/ipv4/ipfrag_low_thresh
$ echo 524288 > /proc/sys/net/ipv4/ipfrag_high_thresh

This is about double the default.

Server threads

See if your server is receiving too many overlapping requests with:

$ grep th /proc/net/rpc/nfsd
  th 8 594 3733.140 83.850 96.660 0.000 73.510 30.560 16.330 2.380 0.000 2.150

The first number is the number of threads available for servicing requests, and the the second number is the number of times that all threads have been needed. The remaining 10 numbers are a histogram showing how many seconds a certain fraction of the threads have been busy, starting with less than 10% of the threads and ending with more than 90% of the threads. If the last few numbers have accumulated a significant amount of time, then your server probably needs more threads.
Increase the number of threads used by the server to 16 by changing RPCNFSDCOUNT=16 in /etc/rc.d/init.d/nfs

Invisible or stale files

If separate clients are sharing information through NFS disks, then you have special problems. You may delete a file on one client node and cause a different client to get a stale file handle. Different clients may have cached inconsistent versions of the same file. A single client may even create a file or directory and be unable to see it immediately. If these problems sound familiar, then you may want to adjust NFS caching parameters and code multiple attempts in your applications.

 

https://help.ubuntu.com/community/HighlyAvailableNFS

Introduction

 

In this tutorial we will set up a highly available server providing NFS services to clients. Should a server become unavailable, services provided by our cluster will continue to be available to users.

Our highly available system will resemble the following: drbd.jpg