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The Linux Kernel Reaches Milestone Version 3.0

Ryan — Wed, 01 Jun 2011 13:36:47 +0000

Since 2004 and for what seems like forever in the technology world, the Linux kernel version has been holding steady at version 2.6.x. The first two numbers were unchanged for nearly 7 years and became largely irrelevant. The third number is the actual version of the kernel. The fourth number accounts for bug and security fixes. But this is all about to change as Linus Torvalds announced the first Release Candidate of the 3.0 code in one of his recent emails.

What will be the shiny new feature in this monumental version? Torvalds announced that the big change was, “NOTHING. Absolutely nothing.”

"The point is that 3.0 is *just* about renumbering, we are very much *not* doing a KDE-4 or a Gnome-3 here. No breakage, no special scary new features, nothing at all like that. We've been doing time-based releases for many years now, this is in no way about features. If you want an excuse for the renumbering, you really should look at the time-based one ('20 years'*) instead,"

And he went on to say:
"But let's face it – what's the point of being in charge if you can't pick the bike shed colour without holding a referendum on it? So I'm just going all alpha-male, and just renumbering it. You'll like it,"

The official release is due out in about six or seven weeks and will be released near the 20th anniversary of Linux.

View system information with /proc/cpuinfo and /proc/meminfo

Ryan — Tue, 09 Dec 2008 12:36:26 +0000

There are 2 files available on a Linux system which will give a user a wealth of information about a system. These files, /proc/cpuinfo and /proc/meminfo are written by the Linux kernel and tell you important details about your cpu and memory.

Both files are read-only and can be viewed with any text editor. This information may be overkill for most users but there are a variety of important fields to look for.

The cpuinfo file provides important stats including model name, cpu cores, cpu MHz, cache size, and flags which show what instruction sets are available on the processor. Systems with multiple processors or multiple cores will have separate entries for each.

Here for example is the output of my /proc/cpuinfo file:

$ cat /proc/cpuinfo

processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 23
model name	: Intel(R) Core(TM)2 Duo CPU     T8300  @ 2.40GHz
stepping	: 6
cpu MHz	: 800.000
cache size	: 3072 KB
physical id	: 0
siblings	: 2
core id	: 0
cpu cores	: 2
apicid		: 0
initial apicid	: 0
fpu		: yes
fpu_exception	: yes
cpuid level	: 10
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good nopl pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr sse4_1 lahf_lm ida
bogomips	: 4787.93
clflush size	: 64
cache_alignment	: 64
address sizes	: 36 bits physical, 48 bits virtual
power management:

processor	: 1
vendor_id	: GenuineIntel
cpu family	: 6
model		: 23
model name	: Intel(R) Core(TM)2 Duo CPU     T8300  @ 2.40GHz
stepping	: 6
cpu MHz	: 800.000
cache size	: 3072 KB
physical id	: 0
siblings	: 2
core id	: 1
cpu cores	: 2
apicid		: 1
initial apicid	: 1
fpu		: yes
fpu_exception	: yes
cpuid level	: 10
wp		: yes
flags		: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx lm constant_tsc arch_perfmon pebs bts rep_good nopl pni monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr sse4_1 lahf_lm ida
bogomips	: 4787.96
clflush size	: 64
cache_alignment	: 64
address sizes	: 36 bits physical, 48 bits virtual
power management:

The important fields to look for in the meminfo file include MemTotal, MemFree, and SwapTotal.

The output of the /proc/meminfo file :

$ cat /proc/meminfo

MemTotal:      4054116 kB
MemFree:       3187648 kB
Buffers:         19852 kB
Cached:         288692 kB
SwapCached:          0 kB
Active:         527556 kB
Inactive:       196060 kB
SwapTotal:           0 kB
SwapFree:            0 kB
Dirty:             208 kB
Writeback:           0 kB
AnonPages:      415096 kB
Mapped:         103684 kB
Slab:            50592 kB
SReclaimable:    23924 kB
SUnreclaim:      26668 kB
PageTables:      15756 kB
NFS_Unstable:        0 kB
Bounce:              0 kB
WritebackTmp:        0 kB
CommitLimit:   2027056 kB
Committed_AS:   870676 kB
VmallocTotal: 34359738367 kB
VmallocUsed:    115908 kB
VmallocChunk: 34359621627 kB
HugePages_Total:     0
HugePages_Free:      0
HugePages_Rsvd:      0
HugePages_Surp:      0
Hugepagesize:     2048 kB
DirectMap4k:     86472 kB
DirectMap2M:   4106240 kB

Upgrade Gentoo Linux Kernel

Ryan — Mon, 10 Nov 2008 13:05:18 +0000

Updating your kernel is important if you want to take advantage of new hardware support or bleeding edge features. Aside from these obvious benefits it also allows you to keep up with security patches, system optimization, and overall stability issues.

The first thing you have to do is emerge the latest gentoo-sources package.

# emerge -u gentoo-sources

The source will now be installed in /usr/src/linux-2.6.27-gentoo-r2. Your specific version will differ from this one of course.

You now need to update the symlink to point to the new sources.

# cd /usr/src
# ln -s linux-2.6.27-gentoo-r2 linux

If your kernel is configured to store a copy of its current configuration in /proc/config.gz you can use those choices to start building your new kernel by copying and uncompressing this stored copy.

# zcat /proc/config.gz > /usr/src/linux/.config

If your current kernel doesn’t support this you can copy the configuration file from the old sources.

# cp /usr/src/linux-2.6.27-gentoo-r2/.config /usr/src/linux/.config

Move to the /usr/src/linux directory.

# cd /usr/src/linux

If you upgrade you kernel on a regular basis you can safely run make oldconfig to configure your new kernel options. This will take your old kernel options and walk you through the configuration changes.

# make oldconfig

If its been awhile use make menuconfig instead. This will give you more context when making configuration choices.

# make menuconfig

Once the new kernel is configured it is time to build it as well as any modules you have specified.

# make && make modules_install

If this completes successfully you new kernel image will be placed here: /usr/src/linux-2.6.27-gentoo-r2/arch/x86_64/boot/bzImage.

Copy this image to the /boot directory. You should rename it to differentiate it from past kernels.

# cp /usr/src/linux-2.6.27-gentoo-r2/arch/x86_64/boot/bzImage /boot/kernel-2.6.27-gentoo-r2

Finally in order to use this image you will have to update your bootloader, such as grub, and add a new entry for the kernel image you have just placed in the /boot directory.

Update grub.conf located here: /boot/grub/grub.conf. Keep your old kernel entry until you have verified your new kernel works correctly.

# New Gentoo Kernel
title Gentoo Linux 2.6.27-r2
root(hd0,0)
kernel /boot/kernel-2.6.27-gentoo-r2 root=/dev/sda0

# old Gentoo Kernel
title Gentoo Linux 2.6.27-r1
root(hd0,0)
kernel /boot/kernel-2.6.27-gentoo-r1 root=/dev/sda0

To use the new kernel reboot and select this new entry at the bootloader screen.

Select threading implementation using LD_ASSUME_KERNEL

Ryan — Mon, 13 Oct 2008 12:37:09 +0000

For backwards compatibility, many Linux distributions support both the older LinuxThreads implementation as well as the newer Native POSIX Thread Library (NPTL). By setting the LD_ASSUME_KERNEL environment variable you can tell the dynamic linker to assume that it is running on top of a particular kernel version. This will override the dynamic linker’s default choice of threading implementation (usually NPTL) and force the use of the older LinuxThreads implementation at run-time.

Many 32-bit systems have 3 separate glibc versions which have support for a minimum OS Application Binary Interface (ABI), designated by a kernel version and offer support for a particular thread implementation.

/lib/tls/libc.so.6

minimum ABI = 2.4.20
Native POSIX Thread Library (NPTL)

/lib/i686/libc.so.6

minimum ABI = 2.4.1
standard LinuxThreads

/lib/libc.so.6

minimum ABI = 2.2.5
early LinuxThreads code which had fixed size threads

It is worth noting that 64-bit systems do not support the older 2.2.5 LinuxThreads implementation.

You can run the following commands to see what thread implementations are supported by each separate glibc library.

$ /lib/tls/libc.so.6 | grep [T|t]hreads

	Native POSIX Threads Library by Ulrich Drepper

$ /lib/i686/libc.so.6 | grep [T|t]hreads

	linuxthreads-0.10 by Xavier Leroy

$ /lib/libc.so.6 | grep [T|t]hreads

	linuxthreads-0.10 by Xavier Leroy

A shared library can tell the dynamic linker which minimum OS ABI version is needed for it to successfully run. At run-time the linker will start at the most recent library path and walk backwards in this order: /lib/tls, /lib/i686, /lib. It will either link to the first library it finds or fail and terminate the program if the minimum ABI is reached before it finds a library.

Setting LD_ASSUME_KERNEL below the minimum threshold ABI version of any dynamic library will cause the linker to skip that library and try to find an older implementation

Set the environment variable by assigning it to a specific ABI/kernel version.

$ export LD_ASSUME_KERNEL=X.Y.Z

You must be careful not to set the the ABI below 2.2.5 in your environment as all programs which require dynamic linking will probably fail to run. Luckily you are still be able to unset or change it back.

It is useless to set LD_ASSUME_KERNEL for most programs as they will run correctly no matter what underlying implementation is used since the API is the same. However there are some programs that may depend on some non-conformant behavior requiring LinuxThreads, which will fail with NPTL.