Databases, Systems & Networks

I want to find out how many times a word (say foo or an IP address) occurs in a text file using the grep command on Linux or Unix-like system?

You can use the grep command to search strings, words, text, and numbers for a given patterns. You can pass the -coption to grep command. It only shows the number of times that the pattern has been matched for each file.

Show the total number of times that the word foo appears in a file named bar.txt

The syntax is:
grep -c string filename
grep -c foo bar.txt
Sample outputs:

3

To count total number of occurrences of word in a file named /etc/passwd root using grep, run:
grep -c root /etc/passwd
To verify that run:
grep --color root /etc/passwd
Pass the -w option to grep to select only an entire word or phrase that matches the specified pattern:
grep -w root /etc/passwd
OR
grep -c -w root /etc/passwd
In this example only match a word being with root:
grep --color -w '^root' /etc/passwd
grep -c -w '^root' /etc/passwd
To show only the matching part of the lines.
grep -o 'root' /etc/passwd
grep -c -o 'root' /etc/passwd
Sample session:

Fig.01: Counting occurrence of words/strings using grep command

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.

To clone a Debian installation, use the apt-clone utility. It’s available (as a separate package, not part of the default installation) in Debian since wheezy and in Ubuntu since 12.04. On the existing machine, run

apt-clone clone foo

This creates a file foo.apt-clone.tar.gz. Copy it to the destination machine, and run

apt-get install apt-clone
apt-clone restore foo.apt-clone.tar.gz

If you’re working with an old system where apt-clone isn’t available, or if you just want to replicate the list of installed packages but not any configuration file, here are the manual steps.

• On the source machine:

cat /etc/apt/sources.list /etc/apt/sources.list.d >sources.list
pkg --get-selections >selections.list
apt-mark auto >auto.list

• On the target machine:

cp sources.list /etc/apt/
apt-get update
/usr/lib/dpkg/methods/apt/update /var/lib/dpkg/
dpkg --set-selections <selections.list
apt-get dselect-upgrade
xargs apt-mark auto <auto.list

I believe that you’re affected by an incompatible change in dpkg that first made it into wheezy. See bug #703092 for background.

The short story is that dpkg --set-selections now only accepts package names that are present in the file /var/lib/dpkg/status or /var/lib/dpkg/available. If you only use APT to manage packages, like most people, then /var/lib/dpkg/available is not kept up-to-date.

After running apt-get update and before running dpkg --set-selections and apt-get -u dselect-upgrade, run the following command:

apt-cache dumpavail >/tmp/apt.avail
dpkg --merge-avail /tmp/apt.avail

From jessie onwards, you can simplify this to

apt-cache dumpavail | dpkg --merge-avail

Alternatively, run

/usr/lib/dpkg/methods/apt/update /var/lib/dpkg/

or even simpler

apt-get install dctrl-tools
sync-available

Another simple method that doesn’t require installing an additional package but will download the package lists again is

dselect update

See the dpkg FAQ for more information. (This is mentioned in the dpkg man page, but more in a way that would remind you of the issue if you were already aware, not in a way that explains how to solve the problem!)

Note that cloning a package installation with dpkg --set-selections doesn’t restore the automatic/manual mark in APT. See Restoring all data and dependencies from dpkg –set-selections ‘*’ for more details. You can save the marks on the source system with

apt-mark showauto >auto.list

and restore them on the target system with

xargs apt-mark auto <auto.list

Securing your server with iptables

In the Getting Started guide, you learned how to deploy a Linux distribution, boot your Linode and perform some basic administrative tasks. Now it’s time to harden your Linode to protect it from unauthorized access.

Update Your System–Frequently

Keeping your software up to date is the single biggest security precaution you can take for any operating system–be it desktop, mobile or server. Software updates frequently contain patches ranging from critical vulnerabilities to minor bug fixes, and many software vulnerabilities are actually patched by the time they become public.

Automatic Security Updates

There are opposing arguments for and against automatic updates on servers. Nonetheless, CentOS, Debian, Fedora and Ubuntu can be automatically updated to various extents. Fedora’s Wiki has a good breakdown of the pros and cons, but if you limit updates to those for security issues, the risk of using automatic updates will be minimal.

The practicality of automatic updates must be something which you judge for yourself because it comes down to what you do with your Linode. Bear in mind that automatic updates apply only to packages sourced from repositories, not self-compiled applications. You may find it worthwhile to have a test environment which replicates your production server. Updates can be applied there and reviewed for issues before being applied to the live environment.

• CentOS uses yum-cron for automatic updates.
• Debian and Ubuntu use unattended upgrades.
• Fedora uses dnf-automatic.

Add a Limited User Account

Up to this point, you have accessing your Linode as the root user. The concern here is that roothas unlimited privileges and can execute any command–even one that could accidentally break your server. For this reason and others, we recommend creating a limited user account and using that at all times. Administrative tasks will be done using sudo to temporarily elevate your limited user’s privileges so you can administer your server without logging in as root.

To add a new user, log in to your Linode via SSH.

CentOS / Fedora

1. Create the user, replacing example_user with your desired username, and assign a password:

   useradd example_user && passwd example_user

2. Add the user to the wheel group for sudo privileges:

   usermod -aG wheel example_user

Debian / Ubuntu

1. Create the user, replacing example_user with your desired username. You’ll then be asked to assign the user a password.

   adduser example_user

2. Add the user to the sudo group so you’ll have administrative privileges:

   adduser example_user sudo

With your new user assigned, disconnect from your Linode as root:

exit

Log back in to your Linode as your new user. Replace example_user with your username, and the example IP address with your Linode’s IP address:

ssh [email protected]

Now you can administer your Linode from your new user account instead of root. Superuser commands can now be prefaced with sudo; for example, sudo iptables -L. Nearly all superuser commands can be executed with sudo, and those commands will be logged to /var/log/auth.log.

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Source: NooBUNBOX

Observium est un système de supervision de réseaux basé sur PHP / MySQL. Il supporte une large gamme de distributions (Windows, Linux, FreeBS, ESXI, etc.) et de matériels (Cisco, Linksys, Juniper, Dell).

Observium se décline en deux versions :

• Observium Community Edition : une version gratuite, open-source et mise à jour tous les 6 mois.
• Observium Profesionnal : une version payante (£150/an) distribuée via svn patchée quotidiennement (bug fixes, mises à jour de sécurité et nouvelles features)

Pour une utilisation non-professionnelle la version Community Edition suffit. Ici nous allons nous intéreser à l’installation et la configuration d’Observium sous debian 7.

Installation d’Observium

Ici nous partons d’une distribution propre, il nous faut donc commencer par installer les dépendances

sudo apt-get install libapache2-mod-php5 php5-cli php5-mysql php5-gd php5-mcrypt php5-json php-pear snmp fping \
mysql-server mysql-client python-mysqldb rrdtool subversion whois mtr-tiny ipmitool graphviz imagemagick

Créez le répertoire ou nous installerons Observium

 sudo mkdir -p /opt/observium && cd /opt

Téléchargez la dernière version du logiciel et extrayez la

sudo wget http://www.observium.org/observium-community-latest.tar.gz
sudo tar zxvf observium-community-latest.tar.gz

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