Databases, Systems & Networks

Source: nixCraft

I have a backup sync program on local server. I have an ssh password less login set up, and I can run commands on an external server in bash script doing:

ssh root@server2 "sync; sync; /sbin/shutdown -h now"

How do I run multiple commands in bash on a remote Unix or Linux server? What is the best Way to SSH in and Run various unix commands in bash?

There are various ways to run multiple commands on a remote Unix server. The syntax is as follows:

Simple bash syntax to run multiple commands on remote machine

Simply run command2 if command1 successful on a remote host called foo
$ ssh bar@foo "command1 && command2"
Run date and hostname commands:
$ ssh user@host "date && hostname"
You can run sudo command as follows on a remote box called server1.cyberciti.biz:
$ ssh -t vivek@server1.dbsysnet.com "sudo /sbin/shutdown -h now"
And, finally:
$ ssh root@server1.dbsysnet.com "sync && sync && /sbin/shutdown -h now"

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Source: nixCraft

What is a « locale » on a Linux operating system? How do I set or get locals (i18n) values on a Linux operating system?

Locales defines language and country specific setting for your programs and shell session. You can use locales to see date, time, number, currency and other values formatted as per your country or language on a Linux or Unix-like system.

To set system’s locale you need use shell variable. For example, LANG variable can be used to set en_US (English US) language.

How do I show current locale settings on a Linux or Unix?

The syntax is:

locale
locale name
locale [options] name

Examples

Simply type the following command:

 $ locale 

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Source: nixCraft

How do I to disable the mail alert send by crontab? When my job is executed and the jobs cannot run normally it will sent an email to root. Why do I receive e-mails to my root account from cron? How can I prevent this? How can I disable email alert sent by cron jobs on a Linux or Unix-like systems?

The crontab command is used to maintain crontab files for individual users. By default the output of a command or a script (if any produced), will be email to your local email account. To stop receiving email output from crontab you need to append following strings at the end of crontab entry.

Cron job prevent the sending of errors and output

To prevent the sending of errors and output, add any one of the following at the end of the line for each cron job to redirect output to a.

/dev/null 2>&1.

OR

&> /dev/null

Cron job example

Edit/Open your cron jobs, enter:

$ crontab -e

Append string >/dev/null 2>&1 to stop mail alert:

0 1 5 10 * /path/to/script.sh >/dev/null 2>&1

OR

0 1 5 10 * /path/to/script.sh &> /dev/null

Save and close the file.

Set MAILTO variable

You can set MAILTO="" variable at the start of your crontab file. This will also disable email alert. Edit/Open your cron jobs:

$ crontab -e

At the top of the file, enter:

MAILTO=""

Save and close the file.

One of the most daunting prospects of administering your own server on a public network is dealing with your server’s security. While security threats in a networked world are real and it is always important to be mindful of security issues, protecting against possible attacks is often a matter of exercising basic common sense and adhering to some general best practices.

This guide takes a broad overview of common security concerns and provides a number of possible solutions to common security problems. You are encouraged to consider deploying some of these measures to “harden” your server against possible attacks.

It’s important to remember that all of the solutions we present in this document are targeted at specific kinds of attacks, which themselves may be relevant only in specific configurations. Security solutions need to be tailored to the kind of services that you’re providing and the software you’re running, and the decision whether or not to deploy a specific security solution is often a matter of personal discretion and cost-benefit analysis.

Perhaps most importantly, it should be understood that security is a process, not a product (credit to Bruce Schneier.) There is no “magic bullet” set of guidelines that can be followed to ensure the security of any system. Threats are constantly evolving, so vigilance is required on the part of network administrators to prevent unauthorized access to systems.

Keep Systems and Software Up To Date

One of the most significant sources of security vulnerabilities are systems running out of date software with known security holes. Make a point of using your system’s package management tools to keep your software up to date; this will greatly assist in avoiding easily preventable security intrusions.

Running system updates with the package management tool, using apt-get update && apt-get upgrade (for Debian and Ubuntu Systems) or yum update (for CentOS and Fedora systems) is simple and straightforward. This practice ensures that if your distribution maintains active security updates, your system will be guarded against many security holes in commonly used software packages.

System update tools will, however, not keep software up to date that you’ve installed outside of package management. This includes software that you’ve compiled and installed “by hand” (e.g. with ./configure && make && make install) and web-based applications that you’ve installed from a software developer’s site, as is often the case with applications like WordPress and Drupal. Also excluded from protection will be libraries and packages you’ve installed with supplementary package management tools like Ruby’s Gems, Perl’s CPAN tool, Python easy_install, and Haskell Cabal. You will have to manage the process of keeping these files up to date yourself.

The method you use to make sure that your entire system is kept up to date is a matter of personal preference, and depends on the nature of your workflow. We would recommend trying very hard to use the versions of software provided by your operating system or other programming platform-specific package management tools. If you must install from “source,” we would recommend that you save the tarballs and source files for all such software in /src/ or ~/src/ so that you can keep track of what software you’ve installed in this manner. Often, you can remove a manually compiled application by issuing make uninstall in the source repository (directory). Additionally, it may be helpful to maintain a list of manually installed software, with version numbers and download locations. You may also want to investigate packaging your own software so that you can install it with apt, yum or pacman.

Because of the complexity of maintaining software outside of the system’s package management tools we strongly recommend avoiding manually installing software unless absolutely necessary. Your choice in a Linux distribution should be heavily biased by the availability of software in that distro’s repositories for the systems you need to run on your server.

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Tarpit + iptables : le Graal?

Un ennemi à part !

Le problème est, ma foi, assez simple :