Highest scored questions

2485 votes

31 answers

542k views

Our security auditor is an idiot. How do I give him the information he wants?

A security auditor for our servers has demanded the following within two weeks: A list of current usernames and plain-text passwords for all user accounts on all servers A list of all password ...

user80776

asked Jul 22, 2011 at 22:44

1811 votes

3 answers

2.1m views

What is a Pem file and how does it differ from other OpenSSL Generated Key File Formats?

I am responsible for maintaining two Debian servers. Every time I have to do anything with security certificates, I Google for tutorials and beat away until it finally works. However, in my searches ...

Noah Goodrich

19.7k

asked May 19, 2009 at 2:24

1427 votes

39 answers

1.2m views

How can I sort du -h output by size

I need to get a list of human readable du output. However, du does not have a "sort by size" option, and piping to sort doesn't work with the human readable flag. For example, running: du | sort -...

Tom Feiner

17.7k

asked Feb 25, 2009 at 13:42

997 votes

15 answers

1.4m views

How to determine if a bash variable is empty?

What is the best way to determine if a variable in bash is empty ("")? I have heard that it is recommended that I do if [ "x$variable" = "x" ] Is that the correct way? (there must be something more ...

Brent

23k

asked May 12, 2009 at 17:54

810 votes

18 answers

2.8m views

Ping a Specific Port

Just a quick sanity check here. Can you ping a specific port of a machine, and if so, can you provide an example? I'm looking for something like ping ip address portNum.

Davie

8,225

asked Oct 8, 2009 at 9:57

784 votes

9 answers

1.1m views

Can scp copy directories recursively?

Currently I can only copy a single .tar file. But how can I copy directories recursively with scp?

kernel

8,591

asked Apr 29, 2011 at 4:24

744 votes

9 answers

2.3m views

How to automate SSH login with password?

How to automate SSH login with password? I'm configuring my test VM, so heavy security is not considered. SSH chosen for acceptable security with minimal configuration. ex) echo password | ssh id@...

Eonil

10.6k

asked Mar 1, 2011 at 11:07

638 votes

18 answers

919k views

How do you find what process is holding a file open in Windows?

One thing that annoys me no end about Windows is the old sharing violation error. Often you can't identify what's holding it open. Usually it's just an editor or explorer just pointing to a relevant ...

cletus

10k

asked May 1, 2009 at 0:47

632 votes

13 answers

164k views

How do I deal with a compromised server?

This is a Canonical Question about Server Security - Responding to Breach Events (Hacking) See Also: Tips for Securing a LAMP Server Reinstall after a Root Compromise? Canonical ...

gunwin

6,420

asked Jan 2, 2011 at 21:31

591 votes

4 answers

333k views

What exactly do the colors in htop status bars mean?

By default, htop shows colored status bars for processors, memory, and swap. From left to right, the bars are colored green, blue, yellow, and red depending on some thresholds. What does it mean when ...

tobym

6,361

asked Sep 13, 2010 at 20:22

569 votes

6 answers

495k views

ssh returns "Bad owner or permissions on ~/.ssh/config"

When I try to ssh to another box, I get this strange error $ ssh hostname Bad owner or permissions on ~/.ssh/config But I made sure that I own and have rw permissions on the file: ls -la ~/.ssh/ ...

Robert

14.7k

asked Mar 29, 2011 at 18:15

555 votes

32 answers

1.1m views

How do I tell Git for Windows where to find my private RSA key?

My Git setup runs fine on Linux, but when I try to set things up under Windows (using Git for Windows and TortoiseGit), I don't know where to put my private SSH key (or, better still, how to tell ssh ...

binaryorganic

6,021

asked Oct 25, 2010 at 16:45

554 votes

11 answers

593k views

In Nginx, how can I rewrite all http requests to https while maintaining sub-domain?

I want to rewrite all http requests on my web server to be https requests, I started with the following: server { listen 80; location / { rewrite ^(.*) https://mysite.com$1 ...

MikeN

8,482

asked Sep 21, 2009 at 14:04

547 votes

5 answers

274k views

What is the difference between double and single square brackets in bash?

I just wondered what exactly the difference between [[ $STRING != foo ]] and [ $STRING != foo ] is, apart from that the latter is POSIX-compliant, found in sh and the former is an extension found in ...

0x89

6,485

asked Aug 9, 2009 at 21:11

499 votes

23 answers

352k views

mysqldump throws: Unknown table 'COLUMN_STATISTICS' in information_schema (1109)

Every time I try to make a mysqldump I get the following error: $> mysqldump --single-transaction --host host -u user -p db > db.sql mysqldump: Couldn't execute 'SELECT COLUMN_NAME, ...

manifestor

6,259

asked May 14, 2018 at 16:40

477 votes

5 answers

1.2m views

What's the default superuser username/password for postgres after a new install?

I have just installed postgres 8.4 on Ubuntu 9.10 and it has never asked me to create a superuser. Is there a default superuser and its password? If not, how do I create a new one?

Thierry Lam

6,281

asked Feb 6, 2010 at 4:54

476 votes

8 answers

186k views

How does IPv4 Subnetting Work?

This is a Canonical Question about IPv4 Subnets. Related: How does IPv6 subnetting work and how does it differ from IPv4 subnetting? How does Subnetting Work, and How do you do it by ...

Community wiki

20 revs, 11 users 40%
Kyle Brandt

466 votes

7 answers

77k views

Something is burning in the server room; how can I quickly identify what it is?

The other day, we notice a terrible burning smell coming out of the server room. Long story short, it ended up being one of the battery modules that was burning up in the UPS unit, but it took a good ...

Chad Harrison

7,010

asked Apr 4, 2013 at 14:22

420 votes

15 answers

760k views

Displaying a remote SSL certificate details using CLI tools

In Chrome, clicking on the green HTTPS lock icon opens a window with the certificate details: When I tried the same with cURL, I got only some of the information: $ curl -vvI https://gnupg.org * ...

Adam Matan

13.4k

asked Jan 23, 2015 at 22:13

416 votes

3 answers

342k views

How do I change my private key passphrase?

I have an existing public/private key pair. The private key is password protected, and the encryption may be either RSA or DSA. These keys are the kind you generate with ssh-keygen and generally store ...

kch

4,632

asked Aug 6, 2009 at 5:37

401 votes

20 answers

443k views

How to run a server on port 80 as a normal user on Linux?

I have Googled about a solution for quite some time, but couldn't find an answer. I am on Ubuntu Linux and want to run a server on port 80, but due to security mechanism of Ubuntu, I get the ...

Deepak Mittal

4,163

asked Nov 10, 2008 at 14:31

390 votes

27 answers

466k views

How can I get the size of an Amazon S3 bucket?

I'd like to graph the size (in bytes, and # of items) of an Amazon S3 bucket and am looking for an efficient way to get the data. The s3cmd tools provide a way to get the total file size using s3cmd ...

Garret Heaton

4,355

asked Nov 15, 2009 at 0:40

389 votes

7 answers

943k views

Why is my crontab not working, and how can I troubleshoot it?

This is a Canonical Question about using cron & crontab. You have been directed here because the community is fairly sure that the answer to your question can be found below. If your question is ...

Eric Leschinski

4,301

asked Nov 17, 2012 at 4:51

378 votes

20 answers

360k views

Showing total progress in rsync: is it possible?

I have searched for this option already, but have only found solutions that involve custom patching. The fact that it does not show in --help and no more info can be found probably indicates the ...

Aron Rotteveel

8,509

asked Jan 5, 2011 at 15:26

378 votes

21 answers

66k views

How do you search for backdoors from the previous IT person?

We all know it happens. A bitter old IT guy leaves a backdoor into the system and network in order to have fun with the new guys and show the company how bad things are without him. I've never ...

Jason Berg

19.2k

asked Aug 18, 2010 at 15:04

373 votes

6 answers

641k views

How to set environment variable in systemd service?

I have an Arch Linux system with systemd and I've created my own service. The configuration service at /etc/systemd/system/myservice.service looks like this: [Unit] Description=My Daemon [Service] ...

lfagundes

3,833

asked Aug 1, 2012 at 19:43

372 votes

6 answers

569k views

What permissions should my website files/folders have on a Linux webserver?

This is a Canonical Question about File Permissions on a Linux web server. I have a Linux web server running Apache2 that hosts several websites. Each website has its own folder in /var/www/. /var/...

Nic

13.5k

asked Feb 6, 2012 at 1:50

366 votes

18 answers

590k views

How do I get the current Unix time in milliseconds in Bash?

How do I get the current Unix time in milliseconds (i.e number of milliseconds since Unix epoch January 1 1970)?

Richard

3,942

asked Jun 14, 2010 at 16:04

362 votes

5 answers

154k views

Anyone else experiencing high rates of Linux server crashes during a leap second day?

*NOTE: if your server still has issues due to confused kernels, and you can't reboot - the simplest solution proposed with gnu date installed on your system is: date -s now. This will reset the ...

Bron Gondwana

1,738

asked Jun 30, 2012 at 16:15

361 votes

29 answers

491k views

How can I use environment variables in Nginx.conf

I have a docker container running Nginx, that links to another docker container. The host name and IP address of the second container is loaded into the Nginx container as environment variables on ...

Hugo Rodger-Brown

3,759

asked Feb 21, 2014 at 15:02

342 votes

4 answers

167k views

What are the functional differences between .profile .bash_profile and .bashrc

What are the functional differences between the .profile, .bash_profile and .bashrc files?

lollercoaster

3,585

asked Apr 20, 2011 at 15:42

340 votes

27 answers

545k views

Can I automatically add a new host to known_hosts?

Here's my situation: I'm setting up a test harness that will, from a central client, launch a number of virtual machine instances and then execute commands on them via ssh. The virtual machines will ...

gareth_bowles

9,207

asked Apr 16, 2010 at 4:15

337 votes

18 answers

432k views

Copying a large directory tree locally? cp or rsync?

I have to copy a large directory tree, about 1.8 TB. It's all local. Out of habit I'd use rsync, however I wonder if there's much point, and if I should rather use cp. I'm worried about permissions ...

Amandasaurus

31.9k

asked Jul 20, 2009 at 14:36

335 votes

5 answers

898k views

How to send ctrl+alt+del using Remote Desktop?

How can I send ctrl+alt+del to a remote computer over Remote Desktop? For example, if I wanted to change the local admin password on a remote PC using a Remote Desktop connection, it would be helpful ...

T. Marshall

3,453

asked Aug 21, 2009 at 15:59

319 votes

2 answers

211k views

Create a public SSH key from the private key?

Let's suppose I have a SSH key, but I've deleted the public key part. I have the private key part. Is there some way I can regenerate the public key part?

Amandasaurus

31.9k

asked Aug 10, 2009 at 14:36

318 votes

27 answers

67k views

100% uptime for a web application

We received an interesting "requirement" from a client today. They want 100% uptime with off-site failover on a web application. From our web application's viewpoint, this isn't an issue. It was ...

NotMe

3,772

asked Sep 29, 2011 at 0:31

313 votes

8 answers

770k views

How to bind MySQL server to more than one IP address?

Is there a secret way to bind MySQL to more than one IP address? As far as I can see the bind-address parameter in the my.cnf does not support more than one IP and you can't have it more than once.

BlaM

3,926

asked Sep 2, 2008 at 16:04

309 votes

5 answers

700k views

Nginx reverse proxy + URL rewrite

Nginx is running on port 80, and I'm using it to reverse proxy URLs with path /foo to port 3200 this way: location /foo { proxy_pass http://localhost:3200; ...

jeffreyveon

3,255

asked Apr 15, 2012 at 17:31

307 votes

14 answers

992k views

What's the command-line utility in Windows to do a reverse DNS look-up?

Is there a built-in command line tool that will do reverse DNS look-ups in Windows? I.e., something like <toolname> w.x.y.z => mycomputername I've tried: nslookup: seems to be forward look-...

alastairs

3,205

asked Jul 15, 2009 at 14:22

301 votes

8 answers

1.4m views

Check if port is open or closed on a Linux server?

How can I check if a port is listening on a Linux server?

James Anderson

3,177

asked Sep 7, 2011 at 17:24

300 votes

4 answers

195k views

How do I select which Apache MPM to use?

This is a Canonical Question about selecting the right Apache httpd MPM. I'm a little confused between the different MPMs offered by Apache - 'worker', 'event', 'prefork', etc. What are the major ...

Tiffany Walker

6,681

asked Apr 26, 2012 at 18:40

296 votes

16 answers

711k views

How to Unban an IP properly with Fail2Ban

I'm using Fail2Ban on a server and I'm wondering how to unban an IP properly. I know I can work with IPTables directly: iptables -D fail2ban-ssh <number> But is there not a way to do it with ...

psp

3,223

asked Jun 29, 2011 at 11:43

290 votes

4 answers

118k views

Why do I need Nginx and something like Gunicorn?

I'm looking for an overly simplified answer to the following question. I'm trying to build a foundational understanding of how Nginx works alongside something like Gunicorn. Do I need both Nginx and ...

a.m.

3,005

asked Nov 15, 2011 at 21:16

286 votes

15 answers

532k views

Finding out what user Apache is running as?

I want to secure a file upload directory on my server as described beautifully here, but I have one problem before I can follow these instructions. I don't know what user Apache is running as. I've ...

Anna

asked Mar 24, 2010 at 16:22

285 votes

5 answers

372k views

What's the difference between IP address 0.0.0.0 and 127.0.0.1?

I know that 127.0.0.1 ~ 127.255.255.254 are the loopback IP addresses for most modern operating systems, and these IP addresses can be used to refer to our own computer. But what's 0.0.0.0? It seems ...

Jichao

3,047

asked Oct 25, 2009 at 7:22

285 votes

5 answers

115k views

Redirect, Change URLs or Redirect HTTP to HTTPS in Apache - Everything You Ever Wanted to Know About mod_rewrite Rules but Were Afraid to Ask

This is a Canonical Question about Apache's mod_rewrite. Changing a request URL or redirecting users to a different URL than the one they originally requested is done using mod_rewrite. This includes ...

Kyle Brandt

84k

asked Dec 20, 2010 at 16:59

283 votes

13 answers

100k views

Can I nohup/screen an already-started process?

I'm doing some test-runs of long-running data migration scripts, over SSH. Let's say I start running a script around 4 PM; now, 6 PM rolls around, and I'm cursing myself for not doing this all in ...

ojrac

2,933

asked Jun 11, 2009 at 22:53

280 votes

160 answers

317k views

Useful Command-line Commands on Windows

The aim for this Wiki is to promote using a command to open up commonly used applications without having to go through many mouse clicks - thus saving time on monitoring and troubleshooting Windows ...

Community wiki

49 revs, 9 users 86%
Sung

279 votes

7 answers

678k views

command for checking Apache configuration

I'm looking for a command that checks the validity of the config files in Apache server on both Debian and RHEL distros. I need to do this prior to restart, so there will be no downtime.

Sigtran

2,893

asked Feb 7, 2011 at 10:14

278 votes

45 answers

68k views

What are the obstacles to providing reliable Internet access and Wi-Fi at large tech conferences? [closed]

Every tech conference I've ever been to, and I've been to a lot, has had absolutely abysmal Wi-Fi and Internet access. Sometimes it's the DHCP server running out of addresses. Sometimes the backhaul ...

Joel Spolsky

3,686

asked Oct 9, 2009 at 1:49

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