Greatest Hits
692
votes
17answers
2.2m 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.
1388
votes
3answers
1.4m 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 ...
448
votes
10answers
1.2m 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@...
2342
votes
30answers
480k 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 ...
776
votes
13answers
1.1m 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 ...
594
votes
10answers
741k views
Can scp copy directories recursively?
Currently I can only copy a single .tar file. But how can I copy directories recursively with scp?
1020
votes
39answers
637k 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 -...
493
votes
31answers
860k 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 ...
388
votes
5answers
896k 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?
137
votes
9answers
961k views
Command line to list users in a Windows Active Directory group?
Is there a command line way to list all the users in a particular Active Directory group?
I can see who is in the group by going to Manage Computer --> Local User / Groups --> Groups and double ...
116
votes
2answers
674k views
What causes the 'Connection Refused' message?
This is a Canonical Question about Connection Refused
We see a lot of questions to the effect
When I try to connect to a system I get a message
Connection refused
Why is this ?
168
votes
5answers
1.1m views
219
votes
6answers
978k 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?
209
votes
5answers
557k 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 ...
161
votes
5answers
851k views
Can you pass user/pass for HTTP Basic Authentication in URL parameters?
I believe this is not possible, but someone I know insisted that it works. I don't even know what parameters to try, and I haven't found this documented anywhere.
I tried http://myserver.com/~user=...
512
votes
11answers
481k 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 ...
149
votes
5answers
235k views
What is the difference between authentication and authorization?
Basic question from a novice:
What is the difference between authentication and authorization?
529
votes
16answers
636k 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 ...
396
votes
5answers
281k 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/
...
304
votes
27answers
280k 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 ...
136
votes
8answers
754k views
Resolve host name from IP address
I'm looking for a command line tool which gets an IP address and returns the host name, for Windows.
143
votes
3answers
169k views
How can I upgrade to Java 1.8 on an Amazon Linux Server?
I tried sudo yum update but it just keeps java "1.7.0_75". I need 1.8 for it to work with another application but can't figure out how to upgrade it.
Do I need to manually install it somehow? There's ...
248
votes
12answers
773k 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-...
56
votes
8answers
514k views
What does “TTL expired in transit” mean on a ping attempt?
We get the message “TTL expired in transit” when we try to ping to a server in a different network segment. When we run tracert, 4 ip addresses repeat themselves indefinitely:
14 60 ms 59 ms ...
217
votes
15answers
663k views
Why do I get “Permission denied (publickey)” when trying to SSH from local Ubuntu to a Amazon EC2 server?
I have an instance of an application running in the cloud on Amazon EC2 instance, and I need to connect it from my local Ubuntu. It works fine on one of local ubuntu and also laptop. I got message "...
27
votes
4answers
214k views
Outlook 2013: how to reset to “first run” status?
TL;DR
Is there a way via script, powershell, reg delete, via telekinesis, whatever to reset Outlook 2013 as if no profiles ever existed and it was running for the first time ever?
Still working ...
84
votes
6answers
678k views
How to determine the hostname from an IP address in a Windows network?
My LAN has 50 Windows hosts. At the Windows command line I try
ping to get the IP address of a running Windows machine.
The question is how to get hostname of a specific IP address in the same ...
152
votes
10answers
399k views
“Add correct host key in known_hosts” / multiple ssh host keys per hostname?
Trying to ssh into a computer I control, I'm getting the familiar message:
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @
@@@@@...
109
votes
4answers
840k views
How to check if a port is blocked on a Windows machine?
On the Windows platform, what native options to I have to check if a port (3306, for example) on my local machine (as in localhost), is being blocked?
147
votes
2answers
312k views
What is Active Directory Domain Services and how does it work?
This is a Canonical Question about Active Directory Domain Services (AD DS).
What is Active Directory? What does it do and how does it work?
How is Active Directory organized: Forest, Child Domain, ...
55
votes
14answers
402k views
Get list of AD groups a user is a member of
Suppose I have the user id of a user in Active Directory. I'd like to get a list of all AD groups in which that user is currently a member of. How can I do this from the Windows command line?
I've ...
89
votes
10answers
647k views
How do I force sync the time on Windows Workstation or Server?
What is the command to sync a Windows workstation or server to its configured time source?
221
votes
7answers
288k views
How to force or redirect to SSL in nginx?
I have a signup page on a subdomain like: https://signup.example.com
It should only be accessible via HTTPS but I'm worried people might somehow stumble upon it via HTTP and get a 404.
My html/...
153
votes
9answers
101k 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, ...
207
votes
11answers
399k 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 ...
153
votes
11answers
347k views
hosts file ignored, how to troubleshoot?
The hosts file on Windows computers is used to bind certain name strings to specific IP addresses to override other name resolution methods.
Often, one decides to change the hosts file, and discovers ...
233
votes
6answers
429k 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 ...
222
votes
15answers
346k 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 ...
232
votes
7answers
387k views
How can I find out what AD groups I'm a member of?
I'm running a Windows XP desktop in a corporate environment. How can I find out what AD groups I belong to?
90
votes
4answers
426k views
Windows Server restart / shutdown history
How can I easily see a history of every time my Windows Server has restarted or shutdown and the reason why, including user-initiated, system-initiated, and system crashed?
The Windows Event Log is ...
318
votes
6answers
401k 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/...
23
votes
8answers
626k views
How to format as FAT32 from Windows 7/Vista
What is the best way to format a USB drive with FAT32 (for Mac compatibility) from within Windows 7/Vista?
I ask because the Disk Management only lets you pick exFAT (because the disk is over 32&...
147
votes
9answers
237k views
Docker Container time & timezone (will not reflect changes)
Where do Docker containers get their time information? I've created some containers from the basic ubuntu:trusty image, and when I run it and request 'date', I get UTC time.
For awhile I got around ...
19
votes
13answers
345k views
Error 0x80070570: How to delete corrupted and unreadable file?
On my system partition I have a folder which cannot be deleted. This folder has been created by restoring files from an Acronis TrueImage backup.
The error message says:
Error 0x80070570: The file ...
110
votes
8answers
564k views
How can I figure out my LDAP connection string?
We're on a corporate network thats running active directory and we'd like to test out some LDAP stuff (active directory membership provider, actually) and so far, none of us can figure out what our ...
126
votes
9answers
732k views
What port should I open to allow remote desktop?
What port(s) should I open/NAT to allow me to use Remote Desktop?
254
votes
16answers
347k 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 ...
159
votes
5answers
321k 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;
...
126
votes
5answers
384k views
VirtualBox: How to set up networking so both host and guest can access internet and talk to each other
I was wondering if someone could give me a simple guide on how to set up virtual networking in VirtualBox (4.0.2) so that the following scenarios work:
Both Host and Guest can access Internet
Host ...
433
votes
2answers
197k 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 ...
