When we do migration, one process will be migrated from one source CPU’s runqueue to destination CPU’s run queue. What is the virtual run time (if CFS is used) after it is moved into destination CPU’s run queue? When the process is dequeued from source CPU’s run queue, its vruntime will minus the minimum vruntime…
In Linux Kernel, we usually trace/debug what kind of events will trigger the phenomena we find in the system. For example, what kind of event will trigger the fact that the timeslice of one process will be very short. In order to solve these kind of problems, we need to output the function stack. Currently,…
I would like to make tee catch the stderr and log it into a file. A brute force method by let tee listen on both stderr and stdout is okay like cmd 2>&1 | tee -a log But how to make tee catch the stderr only? You can make use of “process substitution” (>(…)) to…
In the Go programming language, How to process a file line by line? An equivalent piece of Bash code could be while read line ; do echo $line done < ./input.txt You can make use of the bufio package’s Scan(). // open the file filepath f := os.Open(filepath) // create a scanner fs := bufio.NewScanner(f)…
As is known, keys may be overlap in SST files of level 0 in LevelDB. I am wondering why it needs to be overlap? An sstable is read-only after being written to the disk from a memtable. Accumulated K/Vs in the log up to a certain size are organized as a memtable and written to…
stop-dfs.sh report that there are no datanodes running on some nodes like hdfs-node-000208: no datanode to stop However, there are DataNode process running there. How to clean these processes on many (100s) of nodes? You may use this piece of bash script: for i in `cat hadoop/etc/hadoop/slaves`; do echo $i; ssh $i ‘jps | grep…
What’s the maximum number of mmap()‘ed ranges that a process can makes and how to set the limits on Linux? I have a program that mmap()s and mprotect()s lots ranges. After allocating many ranges, mprotect() starts to fail with ENOMEM error number. From the man page, ENOMEM means 2 possible problems: ENOMEM Internal kernel structures…
Where can I find the source code for the free command on Linux? The source code for the free commands (and many more, like kill, ps, top, sysctl) can be found in procps-ng: https://gitlab.com/procps-ng/procps procps is a set of command line and full-screen utilities that provide information out of the pseudo-filesystem most commonly located at…
Some JavaScript libraries send data by POST instead of JSON. In node.js, how to parse the POST data? You can use the “querystring” module: var qs = require(‘querystring’) The following piece of code works well for me. The comments should help you read the code well. var post_handle = function(request, response) { if (request.method ==…
When fatal error happened, we’d like to kill the program. How to exit the program in Node.js? You can use: process.exit() Here, “process” is a global process object. exit method ends the process. process.exit([code]) Ends the process with the specified code. If omitted, exit uses the ‘success’ code 0. To exit with a ‘failure’ code:…
Firefox has multiple profiles and I am aware of choosing them by invoking firefox with the -P option. But I find that after one firefox instance under one profile is running, even I choose another profile during starting with -P, the new instance is still running under the existing profile. How to run firefox with…
What is the implementation of strstr in glibc? Implementation of STRSTR in glibc (string/strstr.c): /* Return the first occurrence of NEEDLE in HAYSTACK. Return HAYSTACK if NEEDLE is empty, otherwise NULL if NEEDLE is not found in HAYSTACK. */ char * STRSTR (const char *haystack_start, const char *needle_start) { const char *haystack = haystack_start; const…
YouCompleteMe for Vim on Fedora 21 reports this error: [zma@laptop:~/.vim/bundle/YouCompleteMe]$ ./install.sh — The C compiler identification is GNU 4.9.2 — The CXX compiler identification is GNU 4.9.2 — Check for working C compiler: /usr/bin/cc — Check for working C compiler: /usr/bin/cc — works — Detecting C compiler ABI info — Detecting C compiler ABI info…
My program reports that the port is already used. How to find which program or process is listening on a certain port in Linux? You can use netstat to do this. netstat can print network connections. For example, to find which program is listing on port 9999 netstat -pln | grep 9999 You will need…
Some entries in /etc/fstab may not not critical for booting Linux or even not available until Linux has booted. How to avoid the failures or unavailability of some mounting entries in /etc/fstab blocking the boot process of Linux? Please check the tutorial at Controlling Filesystem Mounting on Linux by Playing with /etc/fstab: Allow non-root users…
When should the authors anonymize themselves in a paper submitted to a conference for review? Several general concepts: Peer review is the evaluation of work by one or more people of similar competence to the producers of the work (peers). — Wikipedia Single-blind describes experiments where information that could introduce bias or otherwise skew the…
On my system: $ ulimit -n 1024 Some tools like GATK are aggressive in creating temporary files by creating more than 1000 files under /tmp/. This will cause the program to fail. How to increase the number of files allowed to be opened on Linux? To increase the max number of open files to 10240,…
In Hadoop 2.5.0, I use ‘ps -aux’ and find the Java process has options: -Xmx1000m However, my nodes have 32GB memory. How to make Hadoop Java process heap larger? In yarn-env.sh, you can find: # For setting YARN specific HEAP sizes please use this # Parameter and set appropriately # YARN_HEAPSIZE=1000 In hadoop-env.sh, you can…
This is the scenario: I want to remove a old hard disk which is a LVM PV and contains data. There is free space available on other PVs in the VG. It should move the data from the disk to be removed to other PVs and then remove the disk. The process to remove sdb…
How to display the network usage by processes like top for CPU/mem on Linux? The nethogs tool is my favorite: nethogs – Net top tool grouping bandwidth per process