Linux, programming and more
To see the grub menu on boot, edit the default grub config and decomment the following line:
1 2 | vim /etc/default/grub #GRUB_HIDDEN_TIMEOUT=0 |
This is the default setting with only one identified operating system.
By the way, to force Grub 2 to show the menu on boot just hold down the Shift key while Grub is starting.
In this how to I describe the basically configuration and administration of Postfix on Debian Lenny.
Current I’m using Postfix version 2.5.5
This tutorial should working with older and newer versions.
1 2 | postconf -d | grep "mail_version =" | cut -d" " -f 3 2.5.5 |
You can find the postfix main configuration file under “/etc/postfix”
Let see what wee need to configure a working Internet Mail-Server
1 | postfix ~ # vim /etc/postfix/main.cf |
My example configuration:
1 2 3 4 5 6 7 8 9 10 11 12 13 | myhostname = ipv6.postfix.idrobot.net alias_maps = hash:/etc/aliases alias_database = hash:/etc/aliases mydestination = ipv6.postfix.idrobot.net, localhost.localdomain, localhost mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128 smtp_bind_address6 = 2a01:4f8:101:265::37 mailbox_command = mailbox_size_limit = 0 recipient_delimiter = + inet_interfaces = all inet_protocols = all home_mailbox = Maildir/ bounce_template_file = /etc/postfix/bounce.cf |
If you want to relay your mails to another mail-server you can use the relayhost option:
Edit main.cf, and add this line:
1 | relayhost = ipv6.mx.idrobot.net |
Some administration commands:
Show running config:
1 | postconf -n |
Show the default postfix config instead of running one:
1 | postconf -d |
Show message content:
1 | postcat -q 7FB942082 |
Delete all mail in queue:
1 | postsuper -d ALL |
Schedule immediate delivery:
1 | postqueue -i 7FB942082 |
Flush the queue:
1 | postqueue -f |
This is a very quick guide to setting up a Linux software RAID.
All these examples are same for RAID0 and RAID1
0. Disclaimer
Make sure you back up all your data, or you have empty hdds before you proceed.
1. Disk management
I’m using 2 same HDDs with 400Gigs.
1 2 | Disk /dev/sdb: 400.0 GB, 400088457216 bytes Disk /dev/sdc: 400.0 GB, 400088457216 bytes |
I created on both disks new partitions with parted (also you can use gparted):
1 2 | /dev/sdb1 1 48641 390708801 83 Linux /dev/sdc1 1 48641 390708801 83 Linux |
2. Raid creation
1 2 | $ aptitude update $ aptitude install mdadm |
For RAID-0
1 | $ mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sdb1 /dev/sdc1 |
For RAID-1
1 | $ mdadm --create /dev/md0 --level=1 --raid-devices=2 /dev/sdb1 /dev/sdc1 |
3. Get RAID information
1 2 | $ fdisk -l Disk /dev/md0: 800.1 GB, 800171491328 bytes |
1 2 3 4 5 6 7 | $ cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid0 sdc1[1] sdb1[0] 781417472 blocks 64k chunks unused devices: <none> </none> |
1 2 | $ mdadm --detail --scan ARRAY /dev/md0 level=raid0 num-devices=2 metadata=00.90 UUID=fb3d1fd3:5dd2b871:01f9e43d:ac30fbff |
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 | $ mdadm --detail /dev/md0 /dev/md0: Version : 00.90 Creation Time : Fri Aug 27 21:27:51 2010 Raid Level : raid0 Array Size : 781417472 (745.22 GiB 800.17 GB) Raid Devices : 2 Total Devices : 2 Preferred Minor : 0 Persistence : Superblock is persistent Update Time : Fri Aug 27 22:46:13 2010 State : active Active Devices : 2 Working Devices : 2 Failed Devices : 0 Spare Devices : 0 Chunk Size : 64K UUID : fb3d1fd3:5dd2b871:2ce552e4:6d63ea58 Events : 0.3 Number Major Minor RaidDevice State 0 8 17 0 active sync /dev/sdb1 1 8 33 1 active sync /dev/sdc1 |
4. Create file system
That all you have a running RAID array, to use it you need to create a filesystem for example ext3 one.
1 | mkfs.ext3 /dev/md0 |
Delete RAID array:
1 | mdadm --stop /dev/md0 |
To make sure it doesn’t come back, you need to delete the RAID super blocks…
1 2 | mdadm --misc --zero-superblock /dev/sdb1 mdadm --misc --zero-superblock /dev/sdc1 |
You can mount your raid partition automatically on server start:
1 | vim /etc/fstab |
And add this line to it:
1 | /dev/md0 /mnt ext3 defaults 0 0 |
md0 will automatically mounted to /mnt/
Start a partially built array:
1 2 3 4 5 6 7 | $ mdadm --run /dev/md0 Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid1 sdb1[0] sdc1[1] 390708736 blocks [2/2] [UU] [>....................] resync = 0.0% (277568/390708736) finish=70.3min speed=92522K/sec |
Don’t forget the RAM usage:
I think you have heard already of IPv4 address depletion. A new version of Internet addressing (New Internet protocol) system was prepared many years ago. But since everyone was using IPv4 address, the migration has not been implemented in a large scale. If we continue to use IPv4 address as on today, the entire range would be used up in less than one years. (Hurricane-Electric has a very nice counter.) Public IPv4 addresses are mainly used by Internet servers. Other PCs or Servers can use private IPv4 address which are not reachable from Internet. Although many methods like NAT (Network Address Translation) and CIDR (Classless Inter Domain Routing) were implemented to stretch the IPv4 address usage, it seems that it is reaching a level of saturation now.
It is sure that everyone must migrate to IPv6 address within a couple of months/ years. Some Internet registries are not so liberal in assigning free IPv4 address now. If you want to learn about IPv6 and make sure that you have skills to administer IPv6 address and servers, Hurricane Electric free IPv6 certification is a really great way to begin. You can register for this certification at: he.net. I will give you a brief overview of the tests in the following section.
Through this test set you will be able to:
-> Prove that you have IPv6 connectivity
-> Prove that you have a working IPv6 web server
-> Prove that you have a working IPv6 email address
-> Prove that you have working forward IPv6 DNS
-> Prove that you have working reverse IPv6 DNS for your mail server
-> Prove that you have name servers can respond to queries via IPv6
-> Prove your knowledge of IPv6 technologies through quick and easy testing
There are seven levels of certification available. The breakdown of each are given below:
Newb: Read the primer stuff, be able to answer some quick and easy questions.
Explorer: Verify that you can access ipv6.he.net over IPv6
Enthusiast: Verify that you have an IPv6 capable web server that we can connect to and fetch information from. This should be entered as a FQDN and not an IPv6 address, or you will have issues once you start working on the Guru level.
Administrator: Verify that you have a working IPv6 capable MTA by sending you an email only over IPv6.
Professional: Verify that your MTA has working reverse DNS (ex: dig mx $domain +short ; dig AAAA $mx +short ; dig -x $mx AAAA +short)
Guru: Verify that the authoritative NS for your domain have AAAA records, and respond to queries for the domain (ex: step 1 is dig ns $domain ; dig AAAA $ns | step 2 is dig AAAAA $domain @$nsAAAA)
Sage: Check to see if your domain’s authoritative NS have IPv6 glue with their listed TLD servers. Meaning the TLD server can directly answer for the host record (ex: dig +trace ns $domain to get the TLD server list then dig aaaa $ns @TLD +short for the glue).
After each test you will get a new certificate:
In order to do this, you need to do some sysdmin job:). I am going to specifically focus on Apache and PHP because I’m more of a LAMP user. If you use ASP on Microsofts IIS, I can’t help you (but hey!, Google is there to save your sunny day! :P)
Find your php.ini file in my case,
1 | vim /etc/php5/apache2/php.ini |
Look for the line that says: “expose_php On“
Change it to:
1 | expose_php Off |
Now our PHP is very silent
Note by PHP developer:
; Decides whether PHP may expose the fact that it is installed on the server
; (e.g. by adding its signature to the Web server header). It is no security
; threat in any way, but it makes it possible to determine whether you use PHP
; on your server or not.