Questions and answers.
General question for developers to access data between VM and VMM. As I know, paravirtualization solution is a good way to share data for VM and VMM since it has better performance. Please use Virtio 9p solution for QEMU/KVM. Note that you need to load 9p related modules for guest kernel. Add following in your…
Hello! Im trying to create a screen folder for the user apache, Not root. But it seems to fail, I have no idea on how to fix this issue. I only get the error: Cannot make directory ‘/var/run/screen/S-apache’: Permission denied Im using Cent OS 7 There may be various possible reasons. 2 common reasons: screen…
Just migrated a PHP site to a new server. However, in /var/log/httpd/error_log, there are errors like [:error] [pid 2810] [client 61.92.242.24:43372] PHP Fatal error: Class ‘DOMDocument’ not found in /var/www/…/some.php on line 16 How to add PHP DOMDocument extension to httpd in CentOS 7? You need to install the package php-xml to have DOMCoument support…
How to make iptables/ip6tables configurations permanent across reboot on CentOS 7 Linux? CentOS 7 uses FirewallD by default. If you would like to manage iptables/ip6tables rules directly without using FirewallD, you may use the old good iptables-services service which will load the iptables/ip6tables rules saved in /etc/sysconfig/iptables and /etc/sysconfig/ip6tables when it is started during boot…
Where is MySQL / MariaDB storage location by default on CentOS 7? No special configuration to the MariaDB from official repository of CentOS. On CentOS 7 Linux it is usually by default /var/lib/mysql But here I give you another “hacky” way to find it out. The method is to find out the mysql daemon mysqld’…
How to convert a piece of HTML code to plain text without leading and ending spaces in PHP? For example, I would like to convert <div> <b>hello</b> world</div> to a string hello world You may use this piece of code in PHP to strip HTML tags, remove leading and ending spaces and convert special characters…
vim on CentOS 7 is version 7.4 with patches 1-160: $ vim –version VIM – Vi IMproved 7.4 (2013 Aug 10, compiled Dec 21 2016 17:00:20) Included patches: 1-160 How to upgrade it to version 8 which is the latest major version? Update on Oct 23 2018: the repository introduced in the original method is…
How to get the full request URL of the page being processed in PHP? If you are sure the request is a http or https one, and the PHP script is executed according to (e.g. by a load balancer or apache reverse proxy) the REQUEST_URI/HTTP_HOST which are set by the client, the PHP script can…
How to pause the execution of a process on Linux so that the CPU can be freed? Later, if the node is idle again, how to resume the execution? There are 2 signals related to stopping (pausing) and continuing (resuming) processes: Stop Default action is to stop the process. Cont Default action is to continue…
How to print all fields after a certain field with awk on Linux? Say, I want to print out all fields after field $3: a b c d e f a b b b a a c d should be transformed to d e f b d You may use a for loop in awk…
Some of my pages has XML tags like ‘<?xml ?>’ which are considered by PHP as short open tags ‘<? ?>’. How to disable PHP short open tags? In PHP, to disable the short open tags, you can set the variable short_open_tags = FALSE; in your php.ini. Reference: short_open_tags in php.ini
How to find out all files with replication factor 1 in HDFS? The hdfs dfsadmin -report shows there are blocks with replication factor 1: Missing blocks (with replication factor 1): 7 How to find them out? You can run hdfs fsck to list all files with their replication counts and grep those with replication factor…
How to add a prefix string at the beginning of each line in Bash shell script on Linux? For example, assume we have a file a.txt: line 1 line 2 I want to have, pre line 1 pre line 2 You may use sed, the stream editor for filtering and transforming text: sed -e ‘s/^/pre…
How to detect whether a file is being written by any other process in Linux? Before a program open a file to processes it, it wants to ensure no other processes are writing to it. Here, we are sure after the files are written and closed, they will not be written any more. Hence, one-time…
How to make CentOS Linux to load a module, say ixgbe, automatically at boot time? I am using CentOS 7. You can create a text file <some name>.conf in the /etc/modules-load.d/ and list the modules to be loaded there, one per line. The systemd-modules-load.service daemon will read these files and load the modules. Check more…
It is useful to monitor a server node’s temporary. Among all the sensors’ temperatures, the higher one may be a very important one. How to get the highest temperature from all sensors in a server on Linux? You can use this command to get the the highest temperature from all sensors in a server on…
How to replace strings in a column in a MySQL database table? For example, I would like to replace http://www.systutorials.com with https://www.systutorials.com in a content column of a table post. You may use a SQL statement as follows. update post set content = replace(content, ‘http://www.systutorials.com’, ‘https://www.systutorials.com’) where content like ‘%http://www.systutorials.com%’
WPS’ wpp program reports “libbz2.so.1.0: cannot open shared object file” on CentOS 7 as follows: $ wpp /opt/kingsoft/wps-office/office6/wpp: error while loading shared libraries: libbz2.so.1.0: cannot open shared object file: No such file or directory The reason: wpp will tries to dynamically link ‘libbz2.so.1.0’ $ ldd /opt/kingsoft/wps-office/office6/wpp | grep libbz2 libbz2.so.1.0 => not found libbz2.so.1 =>…
How to count the number of reads in each chromosome in a bam file? The bam file is already sorted by the chromosome names. If the bam file is indexed, you may quickly get these info from the index: samtools idxstats in.bam | awk ‘{print $1″ “$3}’ If the bam file is not indexed, you…
I am happy using encfs on Linux. But how to use encfs on Windows 10? I would suggest EncFS MP. It support Encfs on Windows. Features of EncFSMP: Mounts EncFS folders on Windows and OS X Can create, edit, export and change the password of EncFS folders Is 100% compatible with EncFS 1.7.4 on Linux…