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1500 questions
96
votes
20 answers
What causes SSH error: kex_exchange_identification: Connection closed by remote host?
I setup a SSH server online that is publicly accessible by anyone. Therefore, I get a lot of connections from IPs all over the world. Weirdly, none actually try to authenticate to open a session.
I can myself connect and authenticate without any…
soliz
- 1,061
95
votes
16 answers
Why drop caches in Linux?
In our servers we have a habit of dropping caches at midnight.
sync; echo 3 > /proc/sys/vm/drop_caches
When I run the code it seems to free up lots of RAM, but do I really need to do that. Isn't free RAM a waste?
ivcode
- 1,092
- 1
- 9
- 13
95
votes
1 answer
Explanation of nodev and nosuid in fstab
I see those two options constantly suggested on the web when someone describes how to mount a tmpfs or ramfs. Often also with noexec but I'm specifically interested in nodev and nosuid. I basically hate just blindly repeating what somebody…
Ivan Kovacevic
- 1,931
95
votes
2 answers
Rsync creates a directory with the same name inside of destination directory
When I run this command
rsync -avzp --del -e "ssh -p myport" user@hostname:/var/www/tests /var/www/tests
files get synchronized but instead of saving files in /var/www/tests, Rsync creates one more directory "tests" inside of existing…
javi007
- 953
95
votes
18 answers
What sysadmin things should every programmer know?
As a programmer, we tend to take sysadmins for granted. The few times I've been without a good sysadmin have really made me appreciate what you guys do. When we're venturing into an environment without a sysadmin, what words of wisdom can you…
Nathan DeWitt
- 1,336
95
votes
4 answers
What should I do to make sure that IIS does not recycle my application?
I have a WCF service app hosted in IIS. On startup, it goes and fetches a really expensive (in terms of time and cpu) resource to use as local cache.
Unfortunately, IIS seems to recycle the process on a fairly regular basis. So I am trying to…
AngryHacker
- 2,897
95
votes
6 answers
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 hand, a swap partition bypasses all of the…
Bill Gray
- 1,355
94
votes
5 answers
How to search Powershell command history from previous sessions
I use current Windows 10 with Powershell 5.1. Often, I want to look up commands I have used in the past to modify and/or re-run them. Inevitably, the commands I'm looking for were run in a previous or different PowerShell window/session.
When I…
shawmanz32na
- 1,103
94
votes
3 answers
Modify systemd unit file without altering upstream unit file
I have installed the pimd service by means of apt. This comes with an upstream systemd unit file (/lib/systemd/system/pimd.service).
I want the service to be restarted when for some reason it gets killed, hence I wish to add the line Restart =…
giomanda
- 2,014
94
votes
1 answer
What is ADFS (Active Directory Federation Services)?
So I've been told that our PHP application may need to support authentication using ADFS.
For a non-Microsoft person, what is ADFS?
How does it differ to things like LDAP?
How does it work? What kind of information would be included in a typical…
Simon East
- 1,514
94
votes
2 answers
Does the "bs" option in "dd" really improve the speed?
Every now and then, I'm told that to increase the speed of a "dd" I should carefully choose a proper "block size".
Even here, on ServerFault, someone else wrote that "...the optimum block size is hardware dependent..." (iain) or "...the perfect size…
Damiano Verzulli
- 4,248
94
votes
4 answers
What is the literal escape character in Powershell?
When including a literal quote character inside a quoted string in Powershell, how do I escape the quote character to indicate it is a literal instead of a string delimeter?
David Alpert
- 1,655
94
votes
5 answers
Why do systems generally disable virtualization by default in BIOS settings?
I have yet to see a system whose default configuration enables MMU and directed I/O virtualization. Often this necessitates rebooting and going into the BIOS to enable it if you want, e.g., 64-bit support on your VMs.
Is there some kind of…
John Feminella
- 1,338
94
votes
7 answers
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 ?
Dean Smith
- 1,300
94
votes
15 answers
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 needed to silence the prompt (PS1="") and motd…
rfreytag
- 1,325