• 2.6 offers you the ability to configure the way core files are named through a /proc/sys/kernel/core_pattern file.

• Since Linux 2.5.1 it is possible to atomically move a subtree to another place. The usage is...
  mount --move olddir newdir
  
• Since 2.5.43, dmask=value sets the umask applied to directories only. The default is the umask of the current process. The fmask=value sets the umask applied to regular files only. Again, the default is the umask of the current process.
  
• Directories can now be marked as synchronous using chattr +S, so that all changes will be immediately written to disk. Note, this does not guarantee atomicity, at least not for all filesystems and for all operations. You *can* be guaranteed that system calls will not return until the changes are on disk; note though that this does have has some significant performance impacts.

  EXT3:

• The ext3 filesystem has gained indexed directory support, which offers considerable performance gains when used on filesystems with directories containing large numbers of files.
• In order to use the htree feature, you need at least version 1.32 of e2fsprogs.
• Existing filesystems can be converted using the command
  tune2fs -O dir_index /dev/hdXXX
  
• The latest e2fsprogs can be found at http://prdownloads.sourceforge.net/e2fsprogs

  http://xenotime.net/linux/doc/network-interface-na mes.txt

• The ext2 and ext3 filesystems have new file allocations policies (the "Orlov allocator") which will place subdirectories closer together on-disk. This tends to mean that operations which touch many files in a directory tree are much faster if that tree was created under a 2.6 kernel.

  NFS:

• Basic support has been added for NFSv4 (server and client)
• Additionally, kNFSD now supports transport over TCP. This experimental feature is also backported to 2.4.20

  Profiling:

• A system wide performance profiler (Oprofile) has been included in 2.6. With this option compiled in, you'll get an oprofilefs filesystem which you can mount, that the userspace utilities talk to. You can find out more at http://oprofile.sf.net/
• You need a fixed readprofile utility for 2.6. Present in util-linux as of 2.11z

  CPU frequency scaling:
  

• Certain processors have the facility to scale their voltage/clockspeed. 2.6 introduces an interface to this feature, see Documentation/cpufreq for more information. This functionality also covers features like Intel's speedstep, and the Powernow! feature present in mobile AMD Athlons. In addition to x86 variants, this framework also supports various ARM CPUs. You can find a userspace daemon that monitors battery life and adjusts accordingly at: http://sourceforge.net/projects/cpufreqd

  LVM2 - DeviceMapper:
  

• The LVM1 code was removed wholesale, and replaced with a much better designed 'device mapper'.
• This is backwards compatible with the LVM1 disk format.
• Device mapper does require new tools to manage volumes however. You can get these from ftp://ftp.sistina.com/pub/LVM2/tools/

  From http://www.kniggit.net/wwol26.html:
  

• The number of unique users and groups on a Linux system has been bumped from 65,000 to over 4 billion. (16-bit to 32-bit), making Linux more practical on large file and authentication servers. Similarly, The number of PIDs (Process IDs) before wraparound has been bumped up from 32,000 to 1 billion, improving application starting performance on very busy or very long-lived systems. Although the maximum number of open files has not been increased, Linux with the 2.6 kernel will no longer require you to set what the limit is in advance; this number will self-scale. And finally, Linux 2.6 will include improved 64-bit support on block devices that support it, even on 32-bit platforms such as i386. This allows for filesystems up to 16TB on common hardware.