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1500 questions
62
votes
18 answers

iptables Tips & Tricks

I'm sure Linux sysadmins are quite familiar with iptables, the userland interface to the netfilter packet-filtering framework. Now, this "Question" is meant to be a Community Wiki for collecting together various bits-n-pieces of iptables wisdom.…
pepoluan
  • 5,138
62
votes
3 answers

Unusual HEAD requests to nonsense URLs from Chrome

I have noticed unusual traffic coming from my workstation the last couple of days. I am seeing HEAD requests sent to random character URLs, usually three or four within a second, and they appear to be coming from my Chrome browser. The requests…
JeremyDWill
  • 893
62
votes
4 answers

How to: 1 Cron Job every ODD minutes and 1 other every EVEN minutes?

I have 2 cron jobs, i want one of them to run every odd minute (1,3,5,7,9,11....57,59) and i want the other one to run every even minute (0,2,4,6,8,10,12...58) how can i do it in an easy way? (no scripting - just cron job rules)
wabbajay
  • 629
62
votes
5 answers

What's the difference between 'useradd' and 'adduser'?

What's the difference between useradd and adduser? When/why should I prefer using one or the other?
lindelof
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62
votes
19 answers

Best Practise and Solutions for Sharing Passwords

We have various passwords that need to be known to more than one person in our company. For example, the admin password to our internet routers, the password for our web-host, and also a few "non-IT" passwords like safe codes. Currently, we use an…
Stewart
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61
votes
8 answers

Does bigger capacity SSD have longer life due to wear leveling?

I have been told that you can get a longer lifespan of an SSD if you buy a bigger capacity SSD. The reasoning goes that newer SSDs have wear leveling and thus should sustain the same amount of writing whether you spread this writing on the (logical)…
Ole Tange
  • 3,106
61
votes
4 answers

How to manage DNS in NetworkManager via console (nmcli)?

I have CentOS 7.2 (guest in VirtualBox, vagrant box centos/7, no GUI). I see there is a nameserver in file: $ cat /etc/resolv.conf # Generated by NetworkManager nameserver 10.0.2.3 But how to add or replace with new one? I have done this manually…
Kirby
  • 1,069
61
votes
8 answers

Moving Servers Within The Same Building

Here's my scenario: I'm a developer that inherited (unbeknownst to me) three servers located within my office. I also inherited the job of being the admin of the servers with a distinct lack of server administration knowledge and google /…
Gareth
  • 735
61
votes
1 answer

What does "Connection: close" mean when used in the response message?

When the client uses the Connection: close header in the request message, this means that it wants the server to close the connection after sending the response message. I thought that this header is only used in the request messages, but I have…
user365656
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61
votes
4 answers

What characters should I use or not use in usernames on Linux?

I want to create user accounts named after a domain name. adduser complains that the usernames need to match the NAME_REGEX regular expression. adduser: Please enter a username matching the regular expression configured via the NAME_REGEX…
Ed Haber
  • 765
61
votes
2 answers

What is the ipv6 equivalent of 0.0.0.0/0

When describing IPv4 networks, I can use 0.0.0.0/0 or just 0/0 to specify all networks. What is the equivalent notation for IPv6?
Andrew
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61
votes
4 answers

How to redirect root and only root via htaccess?

I want to redirect only my root to another url, but maintain all the /sub/directories where they belong (and redirect) example: mysite.com/1 redirects to somewhere mysite.com/admin opens a page i want mysite.com/ to redirect to mysecondsite.com and…
jardel
61
votes
6 answers

How to Modify a Cronjob Email Subject

I am running a half dozen different cron jobs from my hosting at Hostmonster.com. When a cronjob has been executed I receive an email with the output of the script. The email comes in the format of: From: Cron Daemon Subject: Cron …
justinl
  • 733
61
votes
4 answers

Mapping UID and GID of local user to the mounted NFS share

I have a server with NFSv4. I am mounting contents of the home folder of remote user to local host. Able to read and write contents, but when I am checking ownership of files at the mounted volume from the local host, they all belongs to…
Alexander
  • 713
61
votes
11 answers

Why do I need to purchase an SSL certificate when I can generate one locally?

I am having trouble understanding why we need to purchase SSL certificates when we can generate them locally using openSSL. What is the difference between the certificate I purchase and a test certificate I generate locally? Is it just a big scam?
S-K'
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