How to get a substring at words boundaries in PHP? For example, for a string $a = “ab cc dde ffg ff”;, I would like to get its substring of length at most 7 from position 0 without breaking words. A simple substring($a, 0, 7) will break the word dde. Here, we consider “words” are…
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 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…
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 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…
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 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…
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…
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 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…
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…
Is encfs available in an Android phone? You may try Encdroid a piece of free software released under the GNU General Public License. It is an Android application. It can access EncFS volumes on cloud storage or internal/USB storage devices. Google Play Store Link: https://play.google.com/store/apps/details?id=org.mrpdaemon.android.encdroid&hl=en Source code: https://github.com/mrpdaemon/encdroid
I have a very large (e.g. 100GB) .gz file and would like to split it into smaller files like 8GB/each for storage/copying. How to split a gzip file to several small ones on Linux? You may use the tool split to split a file by sizes. An example to split a large.tgz to at most…
HDFS stores the metadata of files and blocks in the memory of the NameNode. How to estimate the memory usage of HDFS NameNode for a HDFS cluster? Each file and each block has around 150 bytes of metadata on NameNode. So you may do the calculation based on this. For examples, assume block size is…
Google Map has APIs. But the requirement is that the Map image should be static and uploaded to the website only. No request or dependency on Google’s website should be needed so that the website can run without Internet. Is it possible or allowed (like a screenshot of the Google Map)? If not, any suggestions…
Being sync or async for data writing of a file system or a network file system affects the data integrity. Is Samba sync or async for writes? In summary, Samba writes are async by default. But the behavior is configurable. Here is a great summary by Eric Roseme. Samba defaults to asynchronous writes. smbd writes…
How to get the mtime of a file on Linux from the file’s path? You can use stat to get the file status including the mtime: %y time of last modification, human-readable %Y time of last modification, seconds since Epoch As an example, $ stat -c %y ./file 2017-06-26 13:33:06.764042064 +0800 $ stat -c %Y…