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

learn more… | top users | synonyms (1)

36
votes
3answers
4k views

Why is Linux reporting “free” memory strangely?

This is a canonical question about how Unix operating systems report memory usage. Similar Questions: Server refuses to use swap partition Memory Usage in LINUX I have production ...
36
votes
5answers
86k views

How to install/change locale on Debian?

I've written a web application for which the user interface is in Dutch. I use the system's date and time routines to format date strings in the application. However, the date strings that the system ...
36
votes
10answers
5k views

Run antivirus software on linux DNS servers. Does it make sense?

During a recent audit we were requested to install antivirus software on our DNS servers that are running linux (bind9). The servers were not compromised during the penetration testing but this was ...
36
votes
8answers
61k views

How to interrupt software raid resync?

I want to interrupt a running resync operation on a debian squeeze software raid. (This is the regular scheduled compare resync. The raid array is still clean in such a case. Do not confuse this with ...
36
votes
3answers
5k views

Run command in bash without save in history

How to run command in bash without saving it in history?
36
votes
6answers
37k views

How do I list loaded Linux module parameter values?

Is there a standard way to list the parameter values of a loaded Linux module? I'm essentially probing for another answer to this Linux kernel module parameters question, because the module I'm ...
35
votes
15answers
18k views

Linux - Running The Same Command on Many Machines at Once

I have about a dozen Linux boxes that I occasionally need to run the same command(s) on. Is there an easier way (or automated way) to do this asides from logging on to each machine and running the ...
35
votes
4answers
19k views

Bind to ports less than 1024 without root access

I would like to run applications I'm working on that binds to port numbers less than 1000 without requiring root access. I'm using Linux Mint and have root access to set it up. I would ideally like ...
35
votes
6answers
46k views

shutdown: What is difference between “Power Off” and “Halt”?

With your typical Linux shutdown command, what is the difference between halting the system and powering off the system?
35
votes
1answer
7k views

Why does `tar -xvfz` fail, but `tar xvfz` work?

tar -xvfz foo.tar.gz returns an error tar: z: Cannot open: No such file or directory This is completely understandable - the f switch expects a filename, and so needs to be last. However, omitting ...
34
votes
4answers
70k views

how do you create an ssh key for another user?

I'm trying to create an ssh key for another user. I'm logged in as root. Can I just edit the files generated by ssh-keygen and change root to the user I want?
34
votes
7answers
36k views

Amazon Linux vs. Ubuntu for Amazon EC2 [closed]

I'm setting up my first website on Amazon EC2, and I'm trying to decide which distro to use. I've used Redhat and CentOS in the past, but I have no bias towards any system, I just want to use whatever ...
34
votes
10answers
14k views

Securing a fresh Ubuntu server [closed]

Say I've got a fresh install of Ubuntu, what steps should I take to secure it for use as a Rails application server?
34
votes
5answers
11k views

Can you have more than one ~/.ssh/config file?

We have a bastion server that we use to connect to multiple hosts, and our .ssh/config has grown to over a thousand lines (we have hundreds of hosts that we connect to). This is beginning to get a ...
34
votes
2answers
20k views

Damaged /vmlinuz and /initrd.img symbolic links after Kernel uninstall

OS: Ubuntu 8.04 LTS Server Edition We just rolled back an kernel update using the following command: sudo apt-get remove linux-image-2.6.24-24-server The uninstallation was successful, but it had ...
34
votes
5answers
18k views

Job scheduling using crontab, what will happen when computer is shutdown during that time?

I schedule some tasks using crontab. What will happen if my computer is shutdown or turned off during the time when cron was scheduled to do something? Does each missed cron job run after computer ...
34
votes
4answers
27k views

How to disconnect from lxc-console

I'm working with lxc in Ubuntu 12.04, and it's really great. However, I am unable to disconnect from a lxc-console session after I've connected. I read somewhere that Ctrl-aq will disconnect me from ...
34
votes
3answers
27k views

What's best practice for communication between Amazon EC2 instances?

I've been setting up Amazon EC2 instances for an upcoming project. They are all micro instances, running Ubuntu Server 64bit. Here's what I've setup so far: Web Server -- Apache Database Server ...
33
votes
3answers
22k views

Turn off the Linux OOM killer by default?

The OOM killer on Linux wreaks havoc with various applications every so often, and it appears that not much is really done on the kernel development side to improve this. Would it not be better, as a ...
33
votes
9answers
7k views

Multiple Linux sysadmins working as root

In our team we have three seasoned Linux sysadmins having to administer a few dozen Debian servers. Previously we have all worked as root using SSH public key authentication. But we had a discussion ...
33
votes
5answers
4k views

Smoothest workflow to handle SSH host verification errors?

This is a simple issue that we all face and probably resolve manually without giving much thought. As servers change, are re-provisioned, or IP addresses reallocated, we receive the SSH host ...
33
votes
4answers
18k views

How to make a global ~/.vimrc?

Right now, I make everyone do ~/.vimrc and put their settings there. How can I make a global, default .vimrc for new users?
33
votes
5answers
240k views

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 ...
33
votes
1answer
2k views

Why does removing an unused IP address from an interface kill connections unrelated to that address

Yesterday I did a quick reinstall of a (physical) server in the datacenter, and since I was short on time and with no easy access to our database I just assigned it an IP that I knew was available and ...
33
votes
2answers
3k views

Why was I able to delete a file owned by root in my home directory without being root?

So I was doing some maintenance on my server earlier today and noticed I was able to delete a file owned by root in my home directory. I was able to reproduce a sample: [cbennett@nova ~/temp]$ ls ...
33
votes
5answers
52k views

How passively monitor for tcp packet loss? (Linux)

How can I passively monitor the packet loss on TCP connections to/from my machine? Basically, I'd like a tool that sits in the background and watches TCP ack/nak/re-transmits to generate a report on ...
33
votes
7answers
19k views

filesystem for millions of small files

Which Linux filesystem would you choose for best speed in the following scenario: a hundred million files ~2k file size in average >95% read access pretty random access high concurrency (>100 ...
32
votes
9answers
15k views

How to hide a password passed as command line argument?

I'm running a software daemon that requires for certain actions to enter a passphrase to unlock some features which looks for example like that: $ darkcoind masternode start <mypassphrase> ...
32
votes
3answers
23k views

How to get TX/RX bytes without ifconfig?

Since ifconfig is apparently being deprecated in major Linux distributions, I thought I'd learn something about the ip tool that's supposed to be used instead of ifconfig. And here I ran into a ...
32
votes
4answers
35k views

How to convert line breaks in a text file between the Windows and Unix/Linux formats?

How do I convert line breaks in a text file between the Windows and Unix/Linux formats? I have a *nix environment, but that I need to import and export data with the Windows-style line breaks. I ...
32
votes
4answers
24k views

gpg not enough entropy!

SO I've got a ton of processes running in the background to try and get enough entropy but I am still failing. **We need to generate a lot of random bytes. It is a good idea to perform some other ...
32
votes
3answers
71k views

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 ...
32
votes
4answers
34k views

How to sort ps output by process start time?

Is there a way to sort ps output by process start time, so newest are either at the top or bottom ? On Linux ? On SysV5 ? On Mac ?
32
votes
5answers
46k views

How do I redirect subdomains to a different port on the same server?

I have some subdomains I want to redirect to specific ports on the same server. Say I have dev.mydomain.com I want dev.mydomain.com to transparently redirect to mydomain.com:8080 and I want to ...
32
votes
3answers
33k views

SSL Certificate Location on UNIX/Linux

Is there any standard or convention for where SSL certificates and associated private keys should go on the UNIX/Linux filesystem? Thanks.
32
votes
6answers
29k views

swap partition vs file for performance?

What is better for performance? A partition closer to the inside of the disk will have slower access times, and we must wait for the drive to switch between the OS and swap partitions. On the other ...
31
votes
6answers
5k views

How to create a symbolic link without using ln?

I deleted a critical symbolic link - libc.so.6. I have the file it should point at, but the basic commands such as ln or wget won't work anymore due to the link missing. However, echo or other Bash ...
31
votes
10answers
9k views

Why su to root instead of logging in as root?

I've heard often that it is better to su to root rather than log in directly as the root user (and of course people also say that it's even better to use sudo). I've never really understood why one ...
31
votes
7answers
65k views

How to get e-mail from (failed) cron-jobs in Ubuntu?

I create cron-jobs in Ubuntu by placing the executable in one of /etc/cron.{daily,hourly,monthly,weekly}. There are lots of directories starting with cron: kent@rat:~$ ls -ld /etc/cron* drwxr-xr-x 2 ...
31
votes
3answers
24k views

Linux - How can I see what's waiting for disk IO

I have a server that has a really high load. Nothing is jumping out at me in terms of CPU usage, and it's not swapping. I think it's cause some processes are waiting for disk IO, and I want to see ...
31
votes
6answers
31k views

protocol version mismatch — is your shell clean?

When following the instructions to do rsync backups given here: http://troy.jdmz.net/rsync/index.html I get the error "protocol version mismatch -- is your shell clean?" I read somewhere that I ...
31
votes
6answers
22k views

Merge 2 directory trees in Linux without copying?

I have two directory trees with similar layouts, i.e. . |-- dir1 | |-- a | | |-- file1.txt | | `-- file2.txt | |-- b | | `-- file3.txt | `-- c | `-- file4.txt `-- ...
31
votes
4answers
37k views

run script as user who has nologin shell

All I need to do is to run a specific script as a particual user who does have the nologin/false shell indicated in /etc/passwd. I would run the script as root and this should run as another user. ...
31
votes
5answers
18k views

How useful is mounting /tmp noexec?

Many people (including the Securing Debian Manual) recommend mounting /tmp with the noexec,nodev,nosuid set of options. This is generally presented as one element of a 'defense-in-depth' strategy, by ...
30
votes
5answers
30k views

How to add message that will be read with dmesg?

I am trying to write some custom messages in my dmesg output. I tried: logger "Hello" but this does not work. It exits without error, but no "Hello" appears int the output of: dmesg I am using a ...
30
votes
12answers
58k views

VMware Linux Server — how can you tell if you are a vm or real hardware?

An interesting question. I have logged into a Linux (most likely SuSE) host. Is there some way that I can tell programmatically that I am a VM host or not? Also assume that the vmtools are not ...
30
votes
6answers
19k views

How to determine the “age” of a linux system since installation?

I thought that I could easily check the timestamp of particular files. Then I realized that it wouldn't be so easy when I saw timestamps like 1991.
30
votes
4answers
4k views

Where is the statement of deprecation of ifconfig (on linux)?

A lot of people is stating that the ifconfig command is deprecated in favor of the ipone (on linux at least). This is often used as an argumentation to switch from ifconfig to ip (see some comment ...
30
votes
3answers
32k views

iptables port redirect not working for localhost

I want to redirect all traffic from port 443 to the internal port 8080. I'm using this config for iptables: iptables -t nat -I PREROUTING --source 0/0 --destination 0/0 -p tcp \ --dport 443 ...
30
votes
7answers
37k views

Linux: how to restore config file using apt-get/aptitude?

I've occasionally lost my config file "/etc/mysql/my.cnf", and want to restore it. The file belongs to package mysql-common which is needed for some vital functionality so I can't just purge ...