When uploading a file by the hdfs dfs -put command line in HDFS, how to set a replication factor instead of the global one for that file? For example, HDFS’s global replication factor is 3. For some temporary files, I would like to save just one copy for faster uploading and saving disk space. The…
How to iterate all files and directories under a directory in Python? For example, I would like to iterate each file and directory under /mnt/data/ /mnt/data/ |– file.txt `– great That is: /mnt/data/files.txt /mnt/data/great You can use the os.walk to do this: root, dirs, files = os.walk(path).next() root will be the path.dirs will contain the…
How to get the file extension from a filename in Python? For example, I would like to get “.txt” from “file.txt”. The Python code: >>> name, ext = os.path.splitext(‘file.txt’) >>> name ‘file’ >>> ext ‘.txt’ Manual of os.path.splitext: https://docs.python.org/2/library/os.path.html#os.path.splitext
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 ==…
How to detect the #hash and get the hash in JavaScript? It’s better if no additional library is needed. That said, jquery is fine if it is needed. You can use this piece of JavaScript code: if (window.location.hash) { // hash found var hash = window.location.hash.substring(1); } else { // No hash }
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:…
ssh client can use many authentication methods like password, keys. On a server, I set password-less log in with private/public key. Now, I want to try whether the new password is set correctly by log on using ssh. By default, the key-based authentication method is used again. How to force ssh client to authenticate using…
How to detect whether Linux runs in UEFI or BIOS mode inside the Linux itself without needed to boot the the management console of the mother board? You can detect whether Linux runs in EFI mode by checking whether /sys/firmware/efi exist. In bash, you can test by [ -d /sys/firmware/efi/ ] This technique is used…
We know that we can disable USB 3.0 in the BIOS. But is there a way to force a USB 3.0 port to work in USB 2.0 mode inside of a running Linux? On Linux on some platforms booted in BIOS modes, you can use the following command to force USB 2.0 modes for your…
I tried tree on different Linux boxes to verify the files by diff. However, I found the format can be a little bit different on different nodes. For examples, the tree result could be . |– test2 | |– test4 | `– test5 `– test3 1 directory, 3 files or . ├── test2 │ ├──…
How to test whether the git repository is dirty? git status can show this. But how to diagrammatically detect this in bash? This piece of bash code works like a charm for me: [[ $(git diff –shortstat 2> /dev/null | tail -n1) != “” ]] You can use it to build your script. For example,…
I would like to open files by open() directly. But how to get a FILE pointer from a file descriptor in C on Linux? And how to do the reverse direction: get a file descriptor from a FILE pointer? Get a FILE pointer from a file descriptor (e.g. fd) in C on Linux: FILE *file…
How to open the preferences dialog in Gthumb 3.4 on Linux? There seems no options to open the dialog in the menu on the toolbar. It is in the application menu of gthumb under Gnome 3. Click gthumb application icon on the top left side of you desktop and in the menu you can find…
I am looking for a better method for getting the latest commit’s hash in git. I know git log -1 can show the info of the latest commit and from the info of the latest commit I can use grep and other tools to get the hash. Is there better method supported from git? Note:…
How to configure Linux to use the scanner (not only the printer) in an HP all-in-one printer? The OS is Fedora 22 and the connection between the HP all-in-one printer and the PC is through wireless. The printer is working well. You can check this post for configuring the printer and scanner of HP All-In-One…
How to advertise a different router/gateway ip via DHCP in OpenWRT? In general, you need to configure the DHCP option with code 3 (router). (A list of all options can be found in http://www.networksorcery.com/enp/protocol/bootp/options.htm ) For example, to advise the gateway IP 192.168.1.2, you will send this option: “3,192.168.1.2” Now, for OpenWRT, you have 2…
How to export my Google Chrome password on Linux to a human-readable text file? In newer versions of Chrome, the passwords are stored using the encrypted password storage provided by the system, either Gnome Keyring or KWallet. We need to force Chrome to use a temporary profile folder with unencrypted password storage. Step 1. Connect…
How to find out a domain’s MX record for Email on Linux? For example, to find which domain/IP the email to gmail.com is delivered to. You may make use of the host command. The -t option is used to select the query type. type can be any recognized query type: CNAME, NS, SOA, SIG, KEY,…
I have a Linux web server with Apache (httpd). How to host multiple websites on Apache? To host websites www.example1.com and www.example2.com on a single node with Apache2 on a single IP, you can use VirtualHost as follows. Edit /etc/httpd/conf/httpd.conf and add the following lines: NameVirtualHost *:80 <VirtualHost *:80> DocumentRoot /var/www/example1.com ServerName www.example1.com # Other…
How to allow websites to use .htaccess files in Apache2 web servers? The AllowOverride directive controls this: http://httpd.apache.org/docs/current/mod/core.html#allowoverride To allow AllowOverride in a directory, add the following rules to the /etc/httpd/conf/httpd.conf or similar configuration file for your apache installation: <Directory “/var/www/www.example.com”> Options FollowSymLinks # # AllowOverride controls what directives may be placed in .htaccess files….