Author: Weiwei Jia

How to resize a virtual disk of KVM

ByWeiwei Jia

I test it for qcow2 format. Other formats are TBA. qemu-img resize kvm1.qcow2 +20G cp kvm1.qcow2 kvm1-orig.qcow2 virt-resize –expand /dev/sda1 kvm1-orig.qcow2 kvm1.qcow2 Reference: https://fatmin.com/2016/12/20/how-to-resize-a-qcow2-image-and-filesystem-with-virt-resize/ I test it for qcow2 format. Other formats are TBA. qemu-img resize kvm1.qcow2 +20G cp kvm1.qcow2 kvm1-orig.qcow2 virt-resize –expand /dev/sda1 kvm1-orig.qcow2 kvm1.qcow2 Reference: https://fatmin.com/2016/12/20/how-to-resize-a-qcow2-image-and-filesystem-with-virt-resize/

Why I cannot login remote server with its root

ByWeiwei Jia

# ssh root@192.168.122.96 root@192.168.122.96’s password: Permission denied, please try again. Do according to [1]. NOTE: on Ubuntu, remember to restart ssh service like this “sudo restart ssh”. [1] https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/v2v_guide/preparation_before_the_p2v_migration-enable_root_login_over_ssh

Latex is stuck with a strange problem, see more information for details.

ByWeiwei Jia

$ make pdflatex main.tex This is pdfTeX, Version 3.14159265-2.6-1.40.16 (TeX Live 2015/Debian) (preloaded format=pdflatex) restricted write18 enabled. entering extended mode (./main.tex LaTeX2e <2016/02/01> Babel <3.9q> and hyphenation patterns for 81 language(s) loaded. (/usr/share/texlive/texmf-dist/tex/latex/base/article.cls Document Class: article 2014/09/29 v1.4h Standard LaTeX document class (/usr/share/texlive/texmf-dist/tex/latex/base/size10.clo)) (./usenix.sty (/usr/share/texlive/texmf-dist/tex/latex/psnfss/mathptmx.sty)) (/usr/share/texlive/texmf-dist/tex/latex/graphics/epsfig.sty (/usr/share/texlive/texmf-dist/tex/latex/graphics/graphicx.sty (/usr/share/texlive/texmf-dist/tex/latex/graphics/keyval.sty) (/usr/share/texlive/texmf-dist/tex/latex/graphics/graphics.sty (/usr/share/texlive/texmf-dist/tex/latex/graphics/trig.sty) (/usr/share/texlive/texmf-dist/tex/latex/latexconfig/graphics.cfg) (/usr/share/texlive/texmf-dist/tex/latex/pdftex-def/pdftex.def (/usr/share/texlive/texmf-dist/tex/generic/oberdiek/infwarerr.sty) (/usr/share/texlive/texmf-dist/tex/generic/oberdiek/ltxcmds.sty))))) (/usr/share/texlive/texmf-dist/tex/generic/oberdiek/ifpdf.sty)…

What are the differences between NUMA architecture and SMP architecture?

ByWeiwei Jia

NUMA Architecture: Non-Uniform Memory Access architecture. SMP: Symmetric Multiprocessing architecture. In a Symmetric Multiprocessor, the architectural “distance” to any memory location is the same for all processors, i.e. “symmetric”. In a NonUniform Memory Access machine, each processor is “closer” to some memory locations than others; i.e. memory is partitioned among them Asymmetrically. From my understanding,…

How to get a server’s serial number remotely?

ByWeiwei Jia

How to get a server’s serial number remotely? Tested on Linux Ubuntu 14.04 Trusty > sudo apt-get install dmidecode > sudo dmidecode -s system-serial-number I tried this on several Linux boxes with CentOS 7 and it seems A physical node returns a string like System Serial Number. A KVM VM returns a string like 3fd12bba-12d4-48c7-875a-7a5f57ed8a9a….

Why do I need to run latex/bibtex three times to make everything look good?

ByWeiwei Jia

Why does latex need to be executed 3 times like following? pdflatex main.tex bibtex main pdflatex main.tex pdflatex main.tex Copied from https://tex.stackexchange.com/questions/53235/why-does-latex-bibtex-need-three-passes-to-clear-up-all-warnings. The reason is as follows: 1, At the first latex run, all cite{…} arguments are written in the file document.aux. 2, At the bibtex run, this information is taken by bibtex and the…

How can I login without password and run command in server at a local machine remotely?

ByWeiwei Jia

Login without PWD is fast and efficient. Running commands in server from local machine also have these benefits. login without PWD: add PC A’s public key to PC B’s authorized keys. > a@A:~> cat .ssh/id_rsa.pub | ssh b@B ‘cat >> .ssh/authorized_keys’ > b@B’s password: Run command remotely ssh root@MachineB “ls” NOTE: running commands remotely is…

What is the difference between work conserving I/O scheduler and non-work conserving I/O scheduler?

ByWeiwei Jia

What is the difference between work conserving I/O scheduler and non-work conserving I/O scheduler? In a work-conserving mode, the scheduler must choose one of the pending requests, if any, to dispatch, even if the pending requests are far away from the current disk head position. The rationale for non-work-conserving schedulers, such as the anticipatory scheduler…

How to check interrupts lively in your systems?

ByWeiwei Jia

I need to see what kind of interrupts are handled by which CPU. Please run command: # cat /proc/interrupts or you can execute $ watch -n1 “cat /proc/interrupts” to watch interrupts every 1 second. See [1] [2] for more details. References: [1] https://stackoverflow.com/questions/28301875/how-to-observe-interrupts-in-windows-or-linux-ubuntu-14-04 [2] http://www.linuxjournal.com/content/watch-live-interrupts

How to tune systems to achieve high performance in virtualization circumstances?

ByWeiwei Jia

Most time, we need to tune system parameters to achieve better performance but what the general parameters to be tuned in Linux systems. I think you may want to add following parameters to Kernel boot (/etc/default/grub) parameters intel_idle.max_cstate=0 processor.max_cstate=0 idle=poll intel_pstate=disable At the same time, you may also want to shutdown/open Pause Loop Exiting (PLE)….

How to limit a user’s CPU resources in Linux Systems

ByWeiwei Jia

When you use a server with other users, you might want to limit other users’ CPU resources for some specific aims. Cgroup has lots of parameters we can use to control computer resources. For CPU resources, you can tune cpu.shares parameter to limit users’ CPU resources. To be more precise, change directory to /sys/fs/cgroup/cpu/user and…

How to get vCPU thread ID in QEMU/KVM host OS?

ByWeiwei Jia

In order to collect more information about CPU information internal guest OS, we usually need to get vCPU’s thread ID in host OS. Solution 1: Under directory ‘/sys/fs/cgroup/cpuset/machine’, you will find virtual_machine_name.libvirt-qemu directory. And under this directory, you will find all vCPU sub-directories and under these dirs, you will find vCPU thread IDs. For example…

How to get processes’ I/O utilization percentage

ByWeiwei Jia

Two notices: 1, a process has only one main thread which is itself. 2, a process has many threads. Solution 1: Please use taskstats [1] related interfaces, and send TASKSTATS_TYPE_PID and TASKSTATS_TYPE_TGID commands to kernel to get a process’s ‘blkio_delay_total’ parameter for a process with one main thread and a process with threads separately. Solution…