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1500 questions
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6 answers

Why do ethernet cables have 8 wires?

This might seem a stupid question but why do Ethernet cables have 8 wires? Cat5 cables were just using 4 of the 8 wires, so only 4 are actualy 'needed'. Why not 12 or 16 wires?
ProgrammerAtWork
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65
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18 answers

How to ping in linux until host is known?

How can I ping a certain address and when found, stop pinging. I want to use it in a bash script, so when the host is starting up, the script keeps on pinging and from the moment the host is available, the script continues...
Sander Versluys
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65
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1 answer

Why are my XFS filesystems suddenly consuming more space and full of sparse files?

I've run XFS filesystems as data/growth partitions for nearly 10 years across various Linux servers. I've noticed a strange phenomenon with recent CentOS/RHEL servers running version 6.2+. Stable filesystem usage became highly variable following…
ewwhite
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65
votes
4 answers

best way to debug nginx rewrite rules in config file?

I have a bunch of rewrite rules that I have to port from apache to nginx. It's a rather painful process because I'm not able to see if my rewrite rules and "if" conditions are working as I want them to. Apache did have debugging for its rewrite…
Jiho Kang
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65
votes
3 answers

php cli memory limit

I am getting a memory error in a php cron job: Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 71 bytes) in /opt/matrix/core/lib/DAL/DAL.inc on line 830 The applicable parts of the crontab are: $ sudo crontab -u…
Ryan H
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65
votes
4 answers

How to manage my .ssh/known_hosts file

I run an Ubuntu desktop with a bunch of virtual servers in Virtual Box to test stuff out, etc. In the past I have also been connecting to other kinds of remote VPS Linux boxes. Currently my .ssh/known_hosts file has a whole bunch of keys in it, most…
Luke
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65
votes
5 answers

How can I launch a screen session with a command over ssh on a remote server from my desktop?

I want to be able to launch screen sessions on remote servers from a single ssh command on my desktop. However, screen seems to need a terminal, which is not available when running a command through ssh. So the obvious ssh [email protected] screen…
Thomas Vander Stichele
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65
votes
9 answers

Cannot SSH: debug1: expecting SSH2_MSG_KEX_DH_GEX_REPLY

We have a server on Amazon EC2 running SSH is on a standard (22) port. I placed my public key at the /.ssh/authorized_keys file. The fun thing is that yesterday it was working great! But today, I don't know what happened! I just can't log…
bakytn
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65
votes
5 answers

How do I grant start/stop/restart permissions on a service to an arbitrary user or group on a non-domain-member server?

We have a suite of Windows Services running on our servers which perform a bunch of automated tasks independently of one another, with the exception of one service which looks after the other services. In the event that one of the services should…
abitgone
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65
votes
4 answers

Get a list of SQL Server Agent Jobs

I've got an extensive selection of these to add to a spreadsheet and don't want to go through by hand. What it the T-SQL command(s) to generate a list of SQL Server Agent Jobs?
alimack
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65
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11 answers

Denyhosts vs fail2ban vs iptables- best way to prevent brute force logons?

I'm setting up a LAMP server and need to prevent SSH/FTP/etc. brute-force logon attempts from succeeding. I've seen many recommendations for both denyhosts and fail2ban, but few comparisons of the two. I also read that an IPTables rule can fill the…
spiffytech
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65
votes
12 answers

Subversion error: (405 Method Not Allowed) in response to MKCOL

I am getting the following error while trying to commit a new directory addition. svn: Commit failed (details follow): svn: Server sent unexpected return value (405 Method Not Allowed) in response to MKCOL request for '.... I have never seen this…
Sergio del Amo
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65
votes
16 answers

What is the correct temperature for a server room?

When I was working in our server room, I noticed that it was very cold. I know that the server room has to be cold to offset the heat of the servers, but perhaps it is TOO cold. What is an appropriate temperature to keep our server room at?
freddiefujiwra
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65
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7 answers

Government censors HTTPS traffic to our website. Workarounds?

I am helping run a website that has been blocked for political reasons by the same Russian agency that has previously tried blocking Telegram (RosKomNadzor). This is not the first time it happens, and previously we would just change the domain, but…
Mary
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65
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37 answers

What is the single most influential book every sysadmin should read?

For software developers, there are some books you must absolutely read. What is the single most influential book every programmer should read? How about for sysadmins? Is there a similar list of books?
Gulzar
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