How to set the value of “$releasever” permanently for yum

In a test server I typed “sudo yum update”, it reported errors like:

Then I found this web in google for introducing how to get the value of “$releasever”, but it does not tell us how to set “$releasever” permanently. Therefore, I have to search word like “releasever” in the source code of ‘yum’:

Finally the source code in ‘/usr/lib/python2.6/site-packages/yum/__init__.py’ comes out:

But where does ‘self.conf.yumvar’ get its values? The answer is ‘/etc/yum/vars/’. After

My ‘sudo yum update’ works correctly now.

Vault Conference 2015, in Boston

Vault Conference 2015


vault
Registration

vault
First talk, and the sponsors

vault
John Spray and his talk about development updates of Ceph

vault
I and Coly also give a presentation about our Cold Storage project, the slide is here: Lambert: Achieve High Durability, Low Cost & Flexibility at Same Time β€” open source cold storage engine for ExaBytes data in Alibaba

vault
I am appreciating the help from open source community, seems my oral English is not bad πŸ™‚

128bit atomic operation in arm64

In x86_64 architecture, we could use cmpxchg16b to compare and exchange a 128bit value in one atomic operation. But how to operate a 128bit value in aarch64 architecture (arm64) machine ? The answer is __atomic_compare_exchange().

As below code:

use “gcc test.c -o test” to compile code, but it reports:

The reason is we have not use “libatomic.so”, so use “gcc test.c -o test -latomic” to compile and link the code agin. It works in Fedora 21 (aarch64).

Books I read in year 2014

      No Comments on Books I read in year 2014
Fantastic Mr Fox Buried Cities: Pompeii, Olympia, Mycenae Interstellar ε€ͺι˜³δΈ‹ηš„ι£Žζ™― 周国平散文集

I have watched “Fantastic Mr Fox” four years ago, but just read its novel this year. It’s really a interesting story even I am not a child anymore. The three bad farmers want to kill Mr Fox and his whole family, but Mr Fox just steal their goods without hurting anybody, which is a good idea to me πŸ™‚

“Interstellar” is no doubt the most amazing science fiction this year. This is a story about a father travel a very very long time and space to rescue his children, and also, his descendants. The most attractive part of this novel for me is not those fashion or professional words like “wormhole”, “black hole” etc, but the struggling of the lone father (or the human being). It also give me much power and courage to scrabble out of the traps in my own life.

A fight to save a old server ….

Coly, who is my old colleague, bought a server computer in 2010. This server, which worth about 30,000 Yuan(RMB) 4 years ago, is composed by a ASUS KGPE-D16 motherboard, two AMD-6172 CPUs, and a 670W power supply. Recently, we need many servers to build some software, so I beg Coly to bring his 4 years old server to our small computer room in our office, and he promised.
After installing Linux on this server, I found out that only one CPU could boot up and run, the other one can’t be recognized by operation system. I asked Coly why, and he answered me maybe one CPU was broken.
I thought a mother-board with two sockets can only run one CPU was a great waste; therefore I bought a new CPU and setup it on the mother-board. But after that, the whole server couldn’t boot up totally. Having tried many ways but all failed, I turn to ask Coly to rescue his own old server.
At last, Coly come here and open the lid of the server case, and becomes astonishing very soon.

Coly: What on earth have you done to my server! Have you killed a man who sales silicone grease? You paste too much silicone grease on the CPU, even the edge of the sockets also be contaminated!
Me: Sorry, I just want to make sure the CPU will not be too hot.
Coly: Yeah, they will never be hot now β€”β€” because they can’t even run.

Then, Coly kneels on the floor and begin to clean all the silicon grease on the mother-board, which is a really hard work.

    

But, after clearing, the server still could not boot up.

Coly: Maybe the mother-board has broken, or maybe power supply got a shot-circuit. How much is a KGPE-D16 motherboard in TAOBAO (a very famous e-commerce website in China)? It cost me 8,000 Yuan 4 years ago.
Me: About 800 Yuan.
Coly: ….Mother board becomes cheap so fast. Then, how much is a 670W power supply in TAOBAO? It was 800 Yuan before.
Me: En, about 600 Yuan.
Coly: Ah-ha, looks power supply is a hedging tool for preserving monetary value. I reckon I will buy a large mount of power supply instead of stocks or gold to preserve my money .

In my opinion, a power supply is more stable than a mother board, so I bought a new mother board and luckily boot up the server with two CPU (24 cores). At last, no servers or machines are wasted, in my hand πŸ™‚

Running Fedora 21 on qemu-system-aarch64

Foundation Model V8 is a emulator for ARM64 architecture, but it has many limits, such as slow CPU, small memory (about 2GB), etc. Therefore I want to run fedora on qemu emulator for aarch64. There are already many docs to introduce how to run Foundation Model V8 on Fedora 21 on the web, but none of them could point out the way to run qemu-aarch64 on Fedora 21. Spent about a week, I finally find out the path.

Step 1 Build the edk2 UEFI
Followed this article,you should download the linaro toolchain and edit the “Conf/target.txt”. Then follow these steps to build a file in “Build/ArmVirtualizationQemu-AARCH64/DEBUG_GCC48/FV/QEMU_EFI.fd”

Step 2 Build the qemu-aarch64
I recommend the latest stable QEMU-2.2.0

Now, you have file in “qemu-2.2.0/aarch64-softmmu/qemu-system-aarch64”

Step 3 Download the Fedora 21 image for Foundation Model V8

Now you have “F21-20140829-foundation-v8/F21-20140829-foundation-v8.img”

Step 4 Run the qemu

The Qemu will boot into the UEFI, you could select into the “shell”, in the UEFI shell:

Then you can enter into a grub provided by Fedora 21 and boot into it automaticly.

Step 5 Add the UEFI entry for fedora permanently (optional)

Launch qemu-system-aarch64 by change “-bios xxx” to “-pflash flash0.img -pflash flash1.img” and after enter the UEFI shell:

The UEFI boot entry will write into flash*.img file and the Qemu could boot into Fedora 21 automaticly now.

Run aarch64 binary on x86_64 machines

If we use qemu-arm64-system directly, it will cost too much time on IO and systemcalls.So I try to use SuSE’s userpsace mode qemu, which only reinterprets the arm64 instructions to x86_64 but processes all systemcalls to local host.
This installation manual for user-mode qemu-arm64 has tested on debian-7.7.0

Step 1, make directory for chroot.

Step 2, build qemu of SuSE:

Add this patch to SuSE’s qemu before make it:

Make the qemu and install it:

Step 3, download arm64 disk image of Fedora 19, and extract it.

Copy the qemu-arm64

Step 4, configure the binfmts-misc

and put the content below into /usr/share/binfmts/qemu-arm64 in normal system(not the chroot)

Then run

Step 5, you could chroot into the user mode qemu now:

Now, If you typein “arch”, it will report “aarch64”
Addtionally, add below contents into “aarch64” environtment’s /etc/yum.repos.d/stage4.repo:

You could use yum to install rpm of aarch64 now. If it report DNS unavailable, you could append

into /etc/hosts

I use this user-mode of arm64 Qemu to build linux kernel, but the speed of compiling is not very perfrect. After all, the user-mode Qemu only accelerate the speed of systemcall, not the reinterpreter of instructions. But in my opinion, it is still very useful because it could use host’s resource of network and storage efficiently (Don’t you think it looks like linux-container or lxc/docker ?). If this news is true, I think facebook could use cheap x86_64 machines to test their IOS apps instead of costly Mac minis πŸ™‚

Reflinks:
How to run aarch64 binaries on an x86-64 host using qemu userspace emulation
Arm64Qemu

China Linux Storage & Filesystem 2014 workshop (second day)

The first topic in second day of CLSF 2014 is about NFS, which lead by Tao Peng from PrimaryData. The protocol of NFS is updated to 4.2 and the mainly jobs of NFS community is implement many features (such as “server side copy”) which had been used on local file system onto server side.

nfs

Then the distributed software developer in Xiaomi β€”β€” Liang Xie introduce the basic infrastructure of Xiaomi Cloud Storage and report some severe problems about IO stack. The first problem is that heavy write pressure will cause long latency on ext4 file system, and the latency will be short if the local file system is replaced by xfs.

Zheng Liu (from Alibaba): The implement of journal in xfs is better than ext4. When large mount of write operations come to ext4, it have to write checkpoint in journal and flush disk, which may take a long time. I think you could try ‘no journal’ mode which developed by google guys in ext4.

Another problem is Xiaomi want to use io-scheduler of deadline but they can’t use cgroup by ‘deadline’.

Coly Li (from Alibaba): I suggest that you could try tpps which is a simple and effective io-scheduler in ali_kernel.

Next topic about ext4 is hold by Zheng Liu. In this year, ext4 has add no new features (may be that’s why it is so stable). In google’s chrome OS, they want to store something like cookie for every user, so it need to add encryption feature in ext4. We ask why chrome os not using encryptfs on ext4. The answer of Zheng Liu is: the requirement is came from google itself, so no one knows why. Ext4 also add a new option “sparse_super2” (to store super block only in the beginning and the end of ext4 groups) and “packed_meta_block” (to squeeze all meta data of ext4 into the beginning of disk, mainly for the SMR disk).

ext4

The last topic is about OSv, the most popular and cutting-edge OS in this conference. OSv is a operating system based on virtual machine and cloud environment. It reduce the IO and network stack which makes it very fast and effective. The jvm and some scripts language (such as python, ruby, node.js) could already run on OSv, therefore I consider that it has wined a large part of cloud market for it could run hadoop/spark and many front-end web application.

OSv
OSv
OSv