My tiny mail-command collection of the very important administrator mail command.
You can test E-Mail-Server create scripts with this useful command or send yourself some notifications.
The simplest one: Continue reading ‘Mail command’
Tag Archive for 'Linux'
It’s sometimes useful to prevent some kernel modules from loading. This howto will show you how to do this. This is really easy to do, so if you want you can just skip to the end to see some examples.
Load manualy kernel modules:
1 | modprobe ip_conntrack_ftp |
List all loaded modules:
1 | lsmod |
This option remove loaded module:
1 | modprobe -r pcspkr |
Creating a blacklist:
1 2 | cat /etc/modprobe.d/blacklist-custom blacklist pcspkr |
I show you, how to add a secondary IPv6 Address to your existing one.
You need only to edit “vim /etc/network/interfaces” file and add the IPv6 networking configuration.
1 2 3 4 5 6 7 8 9 10 11 12 13 | # The loopback network interface auto lo iface lo inet loopback # The primary network interface auto eth0 iface eth0 inet static address 10.1.100.4 gateway 10.1.100.1 netmask 255.255.255.0 pre-up modprobe ipv6 post-up ip addr add 2001:470:1f0b:1514::4/64 dev eth0 post-up ip route add default via 2001:470:1f0b:1514::1 dev eth0 |
Another way to do the same:
1 2 3 4 5 6 | pre-up modprobe ipv6 iface eth0 inet6 static address 2001:470:1f0b:1514::4 netmask 64 gateway 2001:470:1f0b:1514::1 |
Also you can put the ipv6 module in to “/etc/modules” instead of “pre-up modprobe ipv6″
Test it:
1 | ping6 ipv6.google.com |
Some complexe example:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 | # The loopback network interface auto lo iface lo inet loopback # The primary network interface allow-hotplug eth0 iface eth0 inet static address 188.40.116.234 netmask 255.255.255.0 network 188.40.116.0 broadcast 188.40.116.255 gateway 188.40.116.206 auto eth0:1 iface eth0:1 inet static address 192.168.2.70 netmask 255.255.255.0 # IPv6 over tunnel-broker auto he-ipv6 iface he-ipv6 inet6 v4tunnel endpoint 216.66.80.30 ttl 255 address 2001:470:1f0a:1604::2 netmask 64 mtu 1480 post-up ip addr add 2001:470:1f0b:1604::1/64 dev eth0 post-up ip route add ::/0 dev he-ipv6 |
I remember being very confused for a very long time about the trailing garbage in commands that I saw in Linux systems.
Now I can explain it to you with a very easy example.
Standard in, out, and error
There are 3 standard sources of input and output for a program. Standard input usually comes from the keyboard if it’s an interactive program, or from another program if it’s processing the other program’s output. The program usually prints to standard output, and sometimes prints to standard error. These three file descriptors (you can think of them as “data pipes”) are often called STDIN, STDOUT and STDERR
Sometimes they’re not named, they’re numbered! The built-in numberings for them are 0, 1, and 2, in that order. By default, if you don’t name or number one explicitly, you’re talking about STDOUT.
Given that context, you can see the command above is redirecting standard output into /dev/null, which is a place you can dump anything you don’t want (often called the bit-bucket), then redirecting standard error into standard output (you have to put an & in front of the destination when you do this).
Will create a new directory
1 | mkdir test |
if you execute it second time you will get a error.
With this redirection you will suppress the error.
1 | mkdir test > /dev/null 2>&1 |
The short explanation, therefore, is “all output from this command should be shoved into a black hole.” That’s one good way to make a program be really quiet! That means, if you have some critical errors in your code, you will never see them.