Databases, Systems & Networks

there’s always apt-cache policy <package-name> (no sudo needed).

Not installed:

olivier@neews:/$ apt-cache policy gnuift
 gnuift:
   Installed: (none)
   Candidate: 0.1.14-11
   Version table:
      0.1.14-11 0
         500 http://archive.ubuntu.com/ubuntu/ oneiric/universe amd64 Packages

Installed:

olivier@neews:/$ apt-cache policy firefox
 firefox:
   Installed: 8.0+build1-0ubuntu0.11.10.3
   Candidate: 8.0+build1-0ubuntu0.11.10.3
   Version table:
  *** 8.0+build1-0ubuntu0.11.10.3 0
         500 http://archive.ubuntu.com/ubuntu/ oneiric-updates/main amd64 Packages
         500 http://archive.ubuntu.com/ubuntu/ oneiric-security/main amd64 Packages
         100 /var/lib/dpkg/status
      7.0.1+build1+nobinonly-0ubuntu2 0
         500 http://archive.ubuntu.com/ubuntu/ oneiric/main amd64 Packages

Or dpkg: dpkg -l | grep -E '^ii' | grep <package name>. When it’s not installed it won’t show output. When it is, it’ll show something like:

olivier@neews:~$ dpkg -l | grep -E '^ii' | grep firefox
 ii  firefox                                                     8.0+build1-0ubuntu0.11.10.3                            Safe and easy web browser from Mozilla
 ii  firefox-branding                                            8.0+build1-0ubuntu0.11.10.3                            Safe and easy web browser from Mozilla - transitional package
 ii  firefox-globalmenu                                          8.0+build1-0ubuntu0.11.10.3                            Unity appmenu integration for Firefox
 ii  firefox-gnome-support                                       8.0+build1-0ubuntu0.11.10.3                            Safe and easy web browser from Mozilla - GNOME support
 ii  firefox-locale-en                                           8.0+build1-0ubuntu0.11.10.3                            English language pack for Firefox

It's obviously a fuzzier search but handy if you're not sure which package you're looking for.
 
 For manually installed things...
 
 A bit harder but if they're on the current path, you could just run them. That's a bit of mission so I'd rather just run:
 
 oli@bert:/$ which chromium-browser
 /usr/bin/chromium-browser

And:

oli@bert:/$ which gnuift
# returns nothing

Which is better?

That depends on the sanity of user. There’s nothing to stop somebody installing something called chromium-browser that isn’t Chromium. They could even package it up incorrectly and install that. Neither method can be 100% certain.

But assuming the owner is sane – packages should be good enough for most people.

What is rsync?

Rsync is a program for synchronizing two directory trees across different file systems even if they are on different computers. It can run its host to host communications over ssh to keep things secure and to provide key based authentication. If a file is already present in the target and is the same as on the source the file will not be transmitted. If the file on the target is different than the one on the source then only the parts of it that are different are transferred. These features greatly increase the performance of rsync over a network.

Lire la suite…

Monitoring Linux server

When it comes to monitoring a Linux server, there are more than enough options to choose from. While there are many production-quality monitoring solutions (e.g., Nagios, Zabbix, Zenoss), boasting of fancy UI, monitoring scalability, comprehensive reporting capabilities, etc., these solutions are probably an overkill for most of us end users. If all you need is to check the basic status (e.g., CPU load, memory usage, active processes, disk usage) of a remote Linux server or desktop, consider linux-dash.

linux-dash is a web-based lightweight monitoring dashboard for Linux machines, which can display, in real-time, various system properties, such as CPU load, RAM usage, disk usage, Internet speed, network connections, RX/TX bandwidth, logged-in users, running processes etc. linux-dash does not come with any backend database for storing long-term statistics. Simply drop in linux-dash app in an existing web server (e.g., Apache, Nginx), and you are good to go. It is a quick and easy way to set up remote monitoring for personal projects.

In this tutorial, I am going to describe how to set up linux-dash in Nginx web server on Linux. Nginx is preferred over Apache web server due to its lightweight engine.

Set up linux-dash on Debian, Ubuntu or Linux Mint

First, install Nginx web server with php-fpm.

$ sudo apt-get install git nginx php5-json php5-fpm php5-curl

Configure Nginx for linux-dash app by creating /etc/nginx/conf.d/linuxdash.conf as follows. In this example, we are going to use port 8080.

$ sudo vi /etc/nginx/conf.d/linuxdash.conf
server {
 server_name $domain_name;
 listen 8080;
 root /var/www;
 index index.html index.php;
 access_log /var/log/nginx/access.log;
 error_log /var/log/nginx/error.log;
 
 location ~* .(?:xml|ogg|mp3|mp4|ogv|svg|svgz|eot|otf|woff|ttf|css|js|jpg|jpeg|gif|png|ico)$ {
 try_files $uri =404;
 expires max;
 access_log off;
 add_header Pragma public;
 add_header Cache-Control "public, must-revalidate, proxy-revalidate";
 }
 
 location /linux-dash {
 index index.html index.php;
 }
 
 # PHP-FPM via sockets
 location ~ .php(/|$) {
 fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
 fastcgi_split_path_info ^(. ?.php)(/.*)$;
 fastcgi_pass unix:/var/run/php5-fpm.sock;
 if (!-f $document_root$fastcgi_script_name) {
 return 404;
 }
 try_files $uri $uri/ /index.php?$args;
 include fastcgi_params;
 }
}

Disable the default site configuration.

$ sudo rm /etc/nginx/sites-enabled/default

Configure php-fpm by editing /etc/php5/fpm/pool.d/www.conf. Make sure to edit « user« , « group » and « listen » directives as shown below. You can keep the rest of the configuration unchanged.

$ sudo vi /etc/php5/fpm/pool.d/www.conf

. . .
user = www-data
group = www-data
listen = /var/run/php5-fpm.sock
. . .

Proceed to download and install linux-dash.

$ git clone https://github.com/afaqurk/linux-dash.git
$ sudo cp -r linux-dash/ /var/www/
$ sudo chown -R www-data:www-data /var/www

Restart Nginx web server as well as php5-fpm to finalize installation.

$ sudo service php5-fpm restart
$ sudo service nginx restart

Lire la suite…

I am a new Ubuntu Linux laptop user. I setup my computer name to ‘tom’ during installation but now I would like to change the computer name to ‘jerry’. Can you tell me how do I I remove tom and set it to jerry on Ubuntu Linux? How do I change the Ubuntu computer name from ‘ubuntu’ to ‘AvlinStar’? Can you tell me more about Ubuntu Linux change hostname command?

You can use the hostname command to see or set the system’s host name. The host name or computer name is usually at system startup in /etc/hostname file. Open the terminal application and type the following commands to set or change hostname or computer name on Ubuntu.

Display the current Ubuntu hostname

Simply type the following command:
$ hostname
Sample outputs:

Ubuntu change hostname command

The procedure to change the computer name on Ubuntu Linux:

1. Type the following command to edit /etc/hostname using nano or vi text editor:
   sudo nano /etc/hostname
   Delete the old name and setup new name.
2. Next Edit the /etc/hosts file:
   sudo nano /etc/hosts
   Replace any occurrence of the existing computer name with your new one.
3. Reboot the system to changes take effect:
   sudo reboot

Sample outputs:

How to change the Ubuntu server hostname without a system restart?

Type the following commands:
$ sudo hostname new-server-name-here
Next edit the /etc/hostname file and update hostname:
$ sudo nano /etc/hostname
Finally, edit the /etc/hosts file and update the lines that reads your old-host-name:
$ sudo nano /etc/hosts
From:
127.0.1.1 old-host-name
To:
127.0.1.1 new-server-name-here
Save and close the file.

Ubuntu Linux Change Hostname Using hostnamectl

Systemd based Linux distro such as Ubuntu Linux 16.04 LTS and above can simply use the hostnamectl command to change hostname. To see current setting just type the following command:
$ hostnamectl
Sample outputs:

   Static hostname: nixcraft
         Icon name: computer-laptop
           Chassis: laptop
        Machine ID: 291893e6499e4d99891c3cf4b70a138b
           Boot ID: 9fda2365b77841649e40a141fde46537
  Operating System: Ubuntu 17.10
            Kernel: Linux 4.13.0-21-generic
      Architecture: x86-64

To change hostname from nixcraft to viveks-laptop, enter:
$ hostnamectl set-hostname viveks-laptop
$ hostnamectl