Ubuntu Linux is a Debian derivative that aims to bring Linux mainstream. Questions on this site should generally refer to Ubuntu Server. Note that http://askubuntu.com is specifically dedicated to Ubuntu questions.

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78
votes
8answers
37k views

Heartbleed: how to reliably and portably check the OpenSSL version?

I was looking at a reliable and portable way to check the OpenSSL version on GNU/Linux and other systems, so users can easily discover if they should upgrade their SSL because of the Heartbleed bug. ...
64
votes
7answers
86k views

How to determine JAVA_HOME on Debian/Ubuntu?

On Ubuntu it is possible to have multiple JVMs at the same time. The default one is selected with update-alternatives. But this does not set the JAVA_HOME environment variable, due to a debian policy. ...
64
votes
11answers
69k views

apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName

I keep getting this warning when I (re)start Apache. * Restarting web server apache2 apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ...
54
votes
1answer
3k views

Can't enter the letter 'e' over ssh [duplicate]

Right now I am experiencing some very, very weird behaviour on a Ubuntu 14.04.2 LTS server I am managing. Connecting to the server over ssh either from cygwin(mintty) or a terminal on a Linux ...
51
votes
11answers
226k views

How to start/stop iptables on Ubuntu?

How can I start/stop the iptables service on Ubuntu? I have tried service iptables stop but it is giving "unrecognized service". Why is it doing so? Is there any other method?
50
votes
5answers
16k views

How does Ubuntu keep track of the “System restart required” flag in motd?

I have a few Ubuntu servers (8.10, 9.10) that is set to automatically install security updates. Some times these updates requires a restart of the system, and this string is shown in motd: *** System ...
46
votes
4answers
20k views

Why don't EC2 ubuntu images have swap?

I started a couple servers on EC2 and they don't have swap. Am I doing something wrong or is it that the machines just don't have any?
45
votes
3answers
12k views

How to remove the “installed manually” flag and revert to “automatically installed” with apt-get?

To compile something, I needed the zlib1g-dev package to be installed so I launched an apt-get install zlib1g-dev. apt-get informed me nicely that the package was already auto-installed because of ...
45
votes
7answers
30k views

Headless Ubuntu server machine sometimes stuck at GRUB menu

I have Ubuntu 10.10 Server installed on a single-board machine in a semi-embedded environment; no keyboard or screen, just SSH access to it. So it's really frustrating when it occasionally boots up ...
44
votes
3answers
16k views

.profile vs. .bash_profile vs. .bashrc

what are the functional differences between these guys?
42
votes
3answers
77k views

How do I upgrade from PHP 5.3 to PHP 5.4.6 in Ubuntu?

Is there an easy way out to get the latest PHP? I have tried updating my package but none of it has 5.4.6 yet... if anyone knows on how to do it quickly, can it be shared here? I've tried compiling ...
38
votes
5answers
3k views

How do I empty /dev/null? [closed]

I am using Ubuntu 10.10. I am generally good with computers but mostly with Windows, I'm not very familiar with Ubuntu. I'm trying to setup a website and I'm talking with a friend I have who works ...
38
votes
4answers
34k views

How do you use apt-get to only install critical security updates on ubuntu?

How do you use apt-get to only install critical security updates on ubuntu? We'd like to only upgrade packages that need to be upgraded for security reasons, without upgrading all other packages.
37
votes
4answers
55k views

Setup ubuntu server to send mail()

I tried searching a lot but unable to find how to actually setup a ubuntu server, so that I can send mails through php using mail() function in php. I have apache2, mysql and php5 installed on my ...
36
votes
7answers
43k views

What is the debian-sys-maint MySQL user (and more)?

I have been bitten several times by the 'debian-sys-maint' user that is installed by default on the mysql-server packages installed from the Ubuntu repositories. Generally what happens is I pull a ...
36
votes
6answers
28k views

How do I permanently disable Linux's console screen saver, system-wide?

I've got an Ubuntu server that boots up in text mode. It rarely has a screen or keyboard attached to it, but when I do attach a screen, I usually have to attach a keyboard too, because the darn ...
35
votes
10answers
13k 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
9answers
57k views

How do I get apt-get to ignore some dependencies?

How do I make apt-get ignore some dependencies? For example, I wanted to install mailx so I can use it to send email from cron scripts/report-generating tools. However, installing mailx also installs ...
34
votes
4answers
31k views

ubuntu apache: httpd.conf or apache2.conf?

which one of these 2 files should i use to configure apache? the httpd.conf is empty while apache2.conf is not. it confuses me!
34
votes
1answer
13k views

How do I ask apt-get to skip any interactive post-install configuration steps?

I have a server build script which uses apt-get to install packages. It then puts pre-written configuration files directly in place, so the interactive post-install configuration dialog in packages ...
31
votes
4answers
103k views

Where to set java heap options (e.g. -Xmx) for Tomcat 6 under Ubuntu 9.04?

I'm running Tomcat using the tomcat6 package from Ubuntu 9.04, which makes a daemon out of Tomcat using jsvc. I'd like to know the proper way to set Java heap options like -Xmx for Tomcat. I'd like to ...
29
votes
7answers
54k 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 ...
29
votes
3answers
13k views

How can I check /dev/xvda1?

On login to EC2 (Ubuntu) instance, I see *** /dev/xvda1 should be checked for errors *** I can't fsck /dev/xvda1 because it is mounted, and sudo umount /dev/xvda1 fails because it is in use. lsof ...
29
votes
3answers
8k views

How do I reattach to Ubuntu Server's 'do-release-upgrade' process?

I accidentally pressed Ctrl+C during Ubuntu Server's do-release-upgrade process. I'd dropped to a shell to compare a .conf file in /etc/. When I pressed Ctrl-C, it asked whether I wanted to try to ...
28
votes
7answers
27k 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 ...
27
votes
4answers
17k views

ssh: “Agent admitted failure to sign using the key”

I'm trying to set up password-less login with ssh on Ubuntu Server, but I keep getting: Agent admitted failure to sign using the key and prompt for password. I have generated new rsa keys. Before ...
27
votes
9answers
11k views

Are configuration management tools (Puppet, Chef) capable of keeping installed packages up to date?

This is probably a simple question for those of you already running configuration management tools. Are configuration management tools such as Puppet or Chef the right approach for keeping installed ...
27
votes
14answers
13k views

File Server - Storage configuration: RAID vs LVM vs ZFS something else…?

We are a small company that does video editing, among other things, and need a place to keep backup copies of large media files and make it easy to share them. I've got a box set up with Ubuntu ...
27
votes
2answers
16k 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 ...
27
votes
8answers
22k views

Why rsync is faster than NFS?

Few days ago I noticed something rather odd (at least for me). I ran rsync copying the same data and deleting it afterwards to NFS mount, called /nfs_mount/TEST. This /nfs_mount/TEST is ...
27
votes
3answers
27k views

list all packages from a repository in ubuntu / debian

is there a command to see what packages are available from a certain ppa repository?
26
votes
7answers
23k views

Unzipping files that are flying in through a pipe

Can I make unzip or any similar programs work on the standard output? The situation is I'm downloading a zip file, which is supposed to be unzipped on the fly. Related issue: ...
26
votes
5answers
27k views

what permission to write PID file in /var/run

Ubuntu touch: cannot touch `/var/run/test.pid': Permission denied I am starting start-stop-daemon and like to write the PID file in /var/run start-stop-daemon is run as my-program-user /var/run ...
26
votes
3answers
22k views

Testing whether jumbo frames are actually working

Is there a command to test whether jumbo frames are actually working? i.e. some sort of "ping" that reports whether or not the packet was broken up along the way. I've an ESXi host with an Ubuntu VM ...
26
votes
8answers
18k views

My server is still vulnerable to heartbleed even after I update OpenSSL

I have an Ubuntu 12.04 server. I have updated the OpenSSL package in order to fix the heartbleed vulnerability. But I am still vulnerable even, even though I have restarted the web server, and even ...
26
votes
4answers
20k 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 ...
25
votes
6answers
91k views

add new user with root access in Linux

I want to add new user and have/grant that new user to have all the root access, how can I do that ? I did sudo adduser --system testuser but this is not working as I expected. Thanks for help.
25
votes
2answers
12k views

Can someone clarify Ubuntu (Debian) dist-upgrade for me?

I've got an Ubuntu 8.04 LTS server. There are several packages which are "kept back" ("the following updates have been kept back:") when I do an apt-get upgrade. It's my understanding that I can do ...
25
votes
8answers
3k views

Ubuntu, how to setup a new machine like an existing one

I have one machine setup with the apps I need, and I'd like to install the same on a new Ubuntu box. Is there a script that will list all the installed apps, so that I can diff between the boxes and ...
25
votes
4answers
59k views

Improving TCP performance over a gigabit network with lots of connections and high traffic of small packets

I’m trying to improve my TCP throughput over a “gigabit network with lots of connections and high traffic of small packets”. My server OS is Ubuntu 11.10 Server 64bit. There are about 50.000 (and ...
24
votes
3answers
14k 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 ...
24
votes
10answers
10k views

Find last time update was performed with apt-get

I need to find the last time that the apt-get update command was run on my server. How can I determine this information?
24
votes
3answers
16k views

How do I auto-start docker containers at system boot?

What is a good way to automatically start docker containers when the system boots up? Is there a preferred way to do this on Ubuntu 14.04? I've used supervisord in the past to auto start web apps. ...
24
votes
5answers
13k 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 ...
24
votes
1answer
12k views

Why does htop have three load averages?

On htop, it shows three load averages, one bold, one normal, one red. What do they signify?
24
votes
2answers
38k views

How to reduce number of sockets in TIME_WAIT?

Ubuntu Server 10.04.1 x86 I've got a machine with a FCGI HTTP service behind nginx, that serves a lot of small HTTP requests to a lot of different clients. (About 230 requests per second in the peak ...
23
votes
9answers
19k views

Calculate MD5 checksum of a directory

I'm looking for a quick way to compare directory contents. Is it possible to do an md5sum (or equivalent checksum) of an entire directory? Using Ubuntu Linux
22
votes
9answers
57k views

How do I find out whether a port is available on Ubuntu 8.04?

Is there any command I can run from bash that will tell me whether a port is already open?
22
votes
8answers
4k views

accidently ran “chown www-data:www-data / -R” as root

i just ran this a few seconds ago, i managed to do ctrl-c as soon as i realized what i started doing. so far in the only dir its started going through is /bin im afraid to do anything else, so far ...
22
votes
6answers
21k views

Why can't I access my CouchDB instance externally on Ubuntu 9.04 server?

Update: I got it working now. Jim Zajkowski's answer helped me detect that my /etc/init.d/couchdb reboot calls weren't actually rebooting the instance. After I manually killed the CouchDB processes ...