If we want to check one program on one remote server, we need to know this server’s IP and port number. How to get this program’s port number in the remote server? # netstat -tulpn Remember to run this program with root permission since some programs can only be accessed by root.
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….
Within a Bash script, how to judge whether its STDERR is redirected to a file in Bash on Linux? For example, ./script.sh /tmp/log 2>&1 Can script.sh detect that its STDERR is redirected? Knowing the destination file is better. To test whether a script’s STDERR (or STDOUT) is redirected to a file, check by [[ -f…
how to set linux date and time in commands For example, to change date to 14 Nov 2017 11:57:00, the command would be, $ sudo date –set “14 Nov 2017 11:57:00” Tue Nov 14 11:57:00 HKT 2017
In Python, os.makedirs() with 0777 mode can not give others write permission The code is as follows $ python Python 2.7.5 (default, Aug 4 2017, 00:39:18) [GCC 4.8.5 20150623 (Red Hat 4.8.5-16)] on linux2 Type “help”, “copyright”, “credits” or “license” for more information. >>> import os >>> os.makedirs(“/tmp/test1/test2”, 0777) >>> The created dirs are not…
How to split a string by string in Python? For example, “a string separated by space” => [“a”, “string”, “separated”, “by”, “space”] and “a,string,separated,by,comma” => [“a”, “string”, “separated”, “by”, “comma”] Python’s string.split() standard library function, if provided a separator, will split the string by the separator, for example >>> str2 = “a,string,separated,by,,,comma” >>> str2.split(“,”) [‘a’,…
How to get the value of a default value if the key does not exist in dict() in Python? We can use the get() function to assign default value if the key does not exist in the dict yet. dict.get(key[, default]) Example as follows. msges = {“msg”: “Hello, World!”} msg = msges.get(“msg”, “”) print(msg) #…
How to install the alien command on CentOS 7 to convert .deb to .rpm? alien is already in EPEL and it makes it quite easy to install it in CentOS 7. First, enable EPEL following this tutorials. Then, install alien by # yum install alien Then alien should be ready: # yum info alien Installed…
How to autohide top and bottom panels in RHEL 7 while application is running I don’t think GNOME 3 or GNOME 3 classic has this function available or there any plugins that supports so. If you need this function that the panel can hide automatically, you may consider another desktop environment, such as MATE, that…
HDFS SecondaraNameNode log shows 2017-08-06 10:54:14,488 ERROR org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode: Exception in doCheckpoint java.io.IOException: Inconsistent checkpoint fields. LV = -63 namespaceID = 1920275013 cTime = 0 ; clusterId = CID-f38880ba-3415-4277-8abf-b5c2848b7a63 ; blockpoolId = BP-578888813-10.6.1.2-1497278556180. Expecting respectively: -63; 263120692; 0; CID-d22222fd-e28a-4b2d-bd2a-f60e1f0ad1b1; BP-622207878-10.6.1.2-1497242227638. at org.apache.hadoop.hdfs.server.namenode.CheckpointSignature.validateStorageInfo(CheckpointSignature.java:134) at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode.doCheckpoint(SecondaryNameNode.java:531) at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode.doWork(SecondaryNameNode.java:395) at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode$1.run(SecondaryNameNode.java:361) at org.apache.hadoop.security.SecurityUtil.doAsLoginUserOrFatal(SecurityUtil.java:415) at org.apache.hadoop.hdfs.server.namenode.SecondaryNameNode.run(SecondaryNameNode.java:357) It seems the checkpoint…
How to force a fsck of a file system, say the root, during the next rebooting of Linux? 2 possible ways: /forcefsck way for / # touch /forcefsck and reboot. Next time the / will be fsck’ed . systemd way Add these 2 kernel boot parameters: fsck.mode=force fsck.repair=yes What these 2 kernel parameters do: KERNEL…
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 flush the STDOUT buffer in Python so that the content wrote to STDOUT is shown immediately? Call the flush library function on sys.stdout which is the STDOUT: import sys sys.stdout.flush() From python doc: flush() Flush the write buffers of the stream if applicable. This does nothing for read-only and non-blocking streams. If you…
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 set one task’s CPU affinity quickly? 1, Get this task’s ID # taskset -pc PID 2, Set this task’s CPU affinity # taskset -c affinity ./task There is also another format # taskset -pc affinity pid For example: set process with PID 3783 to CPU 15 # taskset -pc 15 3783
How to install the gfortran fortran compiler on CentOS 7 Linux? gfortran on CentOS 7 is provided in the gcc-gfortran package. You may install it to install gfortran. # yum install gcc-gfortran Loaded plugins: fastestmirror, langpacks Loading mirror speeds from cached hostfile * base: ftp.cuhk.edu.hk * epel: ftp.cuhk.edu.hk * extras: centos.01link.hk * nux-dextop: li.nux.ro *…
My domain’s email is hosted by DreamHost and all my emails from that domain are sent using DreamHost’s SMTP. How to configure the SPF record for my email domain hosted by DreamHost? For a domain with email and SMTP hosted by DreamHost, you can set its SPF record to v=spf1 include:netblocks.dreamhost.com Reference: What SPF records…
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…
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 disable the fastmirror yum plugin in CentOS 7 Linux? The fastestmirror function of yum is provided by the package `yum-plugin-fastestmirror`. However, because `yum` depends on it, the `yum-plugin-fastestmirror` package can not be removed. If you try to remove it, `yum` will report failures like. # yum remove yum-plugin-fastestmirror Loaded plugins: fastestmirror Resolving Dependencies…