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Questions tagged [linux]

Linux is the generic term for a UNIX-like open source operating system based on the Linux kernel.

GNU/Linux is a UNIX-like Open Source operating system. Linus Torvalds originally wrote the Linux kernel with contributions from others on the MINIX usenet board. Since then, Linux had thousands of developers, both paid by companies and volunteers. The main system tools and libraries for GNU/Linux are sourced from the GNU Project, hence the nomenclature GNU/Linux (GNU Toolchain over Linux Kernel). The Linux kernel is licensed under the GPL v2 license.

There are many different Linux Distributions (sometimes shortened to distro), which consist of software applications packaged and provided with the Linux kernel, being Slackware the oldest active distro and Debian, Red Hat and CentOS among the most used on Internet servers¹.

The Linux kernel is commonly run on servers but is highly portable and is used in a variety of applications, from wireless routers and cell phones to clusters and super computers with thousands of nodes and processors.

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What is the "slash" after the IP?

In Amazon EC2, where I set "security groups", It says: Source: 0.0.0.0/0 And then it gives an example of: 192.168.2.0/24 What is "/24"? I know what port and IP is.
Alex
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How can I allow one user to su to another without allowing root access?

I'd like to allow certain users to su to another user account without having to know that account's password, but not allow access to any other user account (i.e. root). For instance, I'd like to allow Tom the DBA to su to the oracle user, but not…
gharper
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Linux: How to use a file as input and output at the same time?

I've just run the following in bash: uniq .bash_history > .bash_history and my history file ended up completely empty. I guess I need a way to read the whole file before writing to it. How is that done? PS: I obviously thought of using a temporary…
MilliaLover
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Linux: how to explicitly unswap everything possible?

I've launched something that took lots of memory and now everything lags a lot. I guess all applications' memory has gone to swap in order to free some space for the memory-intensive process, and now everything is slowly returning to RAM when…
kolypto
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How to correct Postfix' 'Relay Access Denied'?

This morning, in order to correct a problem with a name mismatch in the security certificate, I followed the recommended steps from How to fix mail server SSL?, but now, when attempting to send an email from a client (in this case the client is…
Noah Goodrich
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Exchange server replacement that runs on Linux

I've worked as a sysadmin for some years and what I keep coming back to is that users like Microsoft Outlook and want to use its Exchange features. I have tried my fair share of commercial alternatives but usually there is either a fundamental…
Andrioid
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How do I delete a route from Linux routing table

This turns out to be harder than I thought. The routes I want to delete are the "!" rejected routes, but I can't seem to formulate the right "route del" command to pull it off. Here is the routing table... Destination Gateway Genmask …
user54259
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Better logging for cronjobs? Send cron output to syslog?

I am looking for a better way to log cronjobs. Most cronjobs tend to spam email or the console, get ignored, or create yet another logfile. In this case, I have a Nagios NSCA script which sends data to a central Nagios sever. This send_nsca script…
Stefan Lasiewski
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Newline-separated xargs

Is it possible to make xargs use only newline as separator? (in bash on Linux and OS X if that matters) I know -0 can be used, but it's PITA as not every command supports NUL-delimited output.
Kornel
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Linux: using find to locate files older than

find has good support for finding files the more modified less than X days ago, but how can I use find to locate all files modified before a certain date? I can't find anything in the find man page to do this, only to compare against another files…
DrStalker
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Should websites live in /var/ or /usr/ according to recommended usage?

According to a guide on the Linux directory structure, /usr/ is for application files, and /var/ is for files that change (I assume this means "files that belong to the applications"). Is this correct? If this is the case then I'm a little torn…
Nick Bolton
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How can I get more info on open pipes show in /proc in Linux?

In Linux if you go digging in /proc//fd often you'll see output like: lrwx------ 1 root root 64 Jul 30 15:14 0 -> /dev/null lrwx------ 1 root root 64 Jul 30 15:14 1 -> /dev/null l-wx------ 1 root root 64 Jul 30 15:14 10 ->…
Kamil Kisiel
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How do I enable non-free packages on Debian?

How can I enable non-free packages on Debian? I want to install Sun's Java JDK but it's not available to me.
Quiffner
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How to check disk I/O utilization per process?

I'm having a problem with a Linux system and I have found sysstat and sar to report huge peaks of disk I/O, average service time as well as average wait time. How could I determine which process is causing these peaks the next time it happen? Is it…
Avada Kedavra
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GNU less: How can I search while ignoring case sensitivity without using less -I option?

From GNU less manpage -i or --ignore-case Causes searches to ignore case; that is, uppercase and lowercase are considered identical. This option is ignored if any uppercase letters appear in the search pattern; in other words, if a pattern contains…
Tom Feiner
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