General Unix
If while booting a Linux DVD/CD you get following message
“No DEFAULT or UI configuration directive found”
then at the boot prompt type the following command:
mboot.c32 -c boot.cfg
works for VMWare ESXi bootable disks
General Unix
To change a username:
usermod -l login-name old-name
To change a UID
usermod -u UID username
do backup all user data before doing this. For a complete change including home directory name, mail spool name etc. read man pages for usermod and groupmod. An example below shows how to kill processes running under old username, display old ID’s info, change the username, change the groupname, the home folder name and Real name, display new ID’s info.
killall -u old
id old
usermod -l new old
groupmod -n new old
usermod -d /home/new -m new
usermod -c “New Real Name” new
id new
To change a user’s home folder name only, use the following usermod command.
usermod -d /path/to/new/homedir/ username
General Unix
several commands exist for this. some are as follows:
for RedHat, CentOS, Fedora
find {/path/to/directory/} -type f -size +{size-in-kb}k -exec ls -lh {} \; | awk '{ print $9 ": " $5 }'
Debian
find {/path/to/directory} -type f -size +{file-size-in-kb}k -exec ls -lh {} \; | awk '{ print $8 ": " $5 }'
$ find ~ -size -500b
# find / -size 20
$ ls -lS
$ ls -lS | less
$ ls -lS | head +10
$ ls -lSr
$ ls -lSr | less
$ ls -lSr | tail -10
General Unix
In some countries where dyndns services are blocked / fire-walled as it happens in China the clients available from Dynamic DNS service providers might not work nor will your router’s built in client. In China I have successfully used ddclient on Linux to achieve automatic updates to my dyndns.org account. I found information about ddclient use from Unix Resources Network and BLUG (Beijing Linux Users Group)
Install ddclient using apt-get (debian)
perform following steps:
1.edit: /etc/ddclient/ddclient.conf
2.run: rc-update add ddclient default
3.run: /etc/init.d/ddclient start
my ddclient.conf was in /etc/ and my entries look like this
use=web, web=ipdetect.dnspark.com, web-skip='Current Address:'
server=members.dyndns.org:8245
login=*******
password='********'
azeems.homeip.net
the first line grabs my IP address from the web.
note the password is between ‘ ‘
members.dyndns.org:8245 bypasses the firewalls and proxies
This method has worked for last two years without failure and highly recommended if you run a linux machine in your network.
General Unix
apt-get install pptpd mc
Type ifconfig and inspect the “eth0” section to find out the IP address of your server [inet addr]
mc -e /etc/pptpd.conf
add two lines:
(Assuming that your internal network IP address is 10.5.1.xxx, geeks call this the 10.5.1.0/24 subnet).
(It is important to avoid using the 192.168.1.xxx subnet for your home because most hotels, Linksys boxes, Cisco boxes, TP-LINK and Trendnet default to 192.168.1.xxx
You cannot VPN from one 192.168.1.0/24 network into another 192.168.1.0/24 network)
localip 10.5.1.3 (this address should be your server’s IP address, [inet addr] when you type ifconfig, see above )
remoteip 10.5.1.241-246
Above configuration assigns 6 IP addresses for 6 roaming users to VPN into your home/corporate network simultaneously.
mc -e /etc/ppp/options
find the line that says ms-dns, modify the IP addresses to suit your local environment.
These two IP addresses should be the IP addresses of the DNS servers provided to you by your ISP or use your router if that does the DNS for your network.
The following examples are the OpenDNS servers which anyone can use.
ms-dns 208.67.222.222
ms-dns 208.67.220.220
Create user accounts and passwords for roaming/telecommuting users to access your VPN server (use strong passwords for security)
mc -e /etc/ppp/chap-secrets
e.g.
alice pptpd a-strong-password *
bob pptpd another-strong-password *
The trailing * means these users are allowed to come in from any IP address, if the telecommuter or branch office
has a static or fixed IP address and never roams, then you can replace the * with his/her fixed IP address (or IP address block) for added security.
You typically want to use a “static IP” address for VPN server behind firewall.
Change the Debian box from DHCP to static IP address:
mc -e /etc/network/interfaces
find the line that says iface eth0 inet dhcp
change the above line to iface eth0 inet static
add 4 lines below the iface eth0 inet static line, the actual addresses you use should be your own internal network environment.
address 10.5.1.3
netmask 255.255.255.0
broadcast 10.5.1.255
gateway 10.5.1.1
F2 to save the file, F10 to quit editing
mc -e /etc/resolv.conf
nameserver 216.21.128.22 (note: please use your ISP/cable/DSL company’s DNS servers)
nameserver 216.21.129.22
F2 to save the file, F10 to quit editing.
reboot
One final tweak is to instruct the Linux kernel to “forward” VPN packets.
mc -e /etc/sysctl.conf
fine the line that says:
#net.ipv4.conf.default.forwarding=1
delete the #
save the file.
reboot
With older kernels, you may need to add these (depreciated) steps:
touch /etc/init.d/pptp
chmod 755 /etc/init.d/pptp
mc -e /etc/init.d/pptp edit the file, add one line, save the file.
echo 1 > /proc/sys/net/ipv4/ip_forward
cd /etc/rcS.d
ln -s /etc/init.d/pptp S85-pptp-packet-forward
reboot
General Unix
This can be a challenging process depending on which distro you are installing. The challenge comes from the fact that Mac’s uses EFI (old PPC ones use Open Firmware) instead of old fashion BIOS. I spent some time getting Debian Squeeze onto a Mac Pro and in the process found some information which is listed below:
– All of the install process for any linux distro is same as for any box. The only part where it gets difficult is partition and boot loader. If your distro install does not let you perform manual partition and let you choose the boot loader as well as where it installs then you need to choose Expert Install when booting from the installation media.
– You should also get hold of rEFIt either on a USB or CD. You will need it later. There are various other ways I found but using rEFIt was easy and quick.
In my experience (Debian Squeeze) no matter how I tried GRUB boot loader gave issues. Even rEFIt complained. There is a way of using a MAC OS X install CD to bless the Linux partition but using LILO was easy. If you want to use Bless command it is as follows:
$ sudo bless --mount /efi --setBoot --file /efi/efi/refit/refit.efi --labelfile /efi/efi/refit/refit.vollabel
considering the partition on which you copy rEFIt files is mounted as /efi
There is a guide if you want to follow this at:
http://wiki.debian.org/InstallingDebianOn/Apple/MacBookAir/squeeze
During the installation if you want to clean the MBR use the following commands to remove all bootloaders from MBR
use dd command from a shell (it removes partition table as well):
# dd if=/dev/null of=/dev/sdX bs=512 count=1
Just remove MBR, without the partition table:
# dd if=/dev/null of=/dev/sdX bs=446 count=1
What I did was to start expert install, create first partition of max. 100MB with FAT16 system and tag it as “do not mount”. Then the second partition will be of max. 500MB with ext2 or ext3, mount will be /boot and tag it bootable. Now create a swap and then root where everything else is mounted. After basic OS and then software install when it comes to bootloader install Lilo (elilo failed to install) and got it written to the MBR. Finish the installation and Mac will reboot. Boot with rEFIt CD and choose to start the partition created (2nd icon from left on the bottom line – one just right to the shell icon). It should not report any error, will you to MBR before and after the change and will request your permission to make the change. Allow it and reboot. Voila… Lilo should boot your Linux after about 10-15 seconds wait on the first white screen.
General Unix
Some new servers have BIOS based RAID instead of using a proper RAID controller. In this case you might have to use software raid. During installation when you are at the disk partition step choose customised partitioning. Assuming Linux is your single OS on the system, you have identical drives (you don’t really need them identical as long as equal space is available on all partitions) follow the steps below – example screen shots are from CentOS installation.
1) Upon entering the partitioning review, it should looks like this:
2) Next is to delete every partition and left with only free space for both hard disk. It should looks like this:
3) So click the New button (or the F2 button) to start creating new partition. Straight away change the File System Type into Software RAID. In the Allowable Drives, please select SDA first, somehow CentOS won’t work if we select both hard disk at the same time. Put100 for the Size as we want to create the space for boot first. Click the Ok button after finished:
4) Just do exactly the same like Step 3, but this time choose the SDB instead. Press Ok when done:
5) Next is the swap partition for the RAID. Click the New button and choose the File System Type to Software RAID. Choose SDA first for the Allowable Drives. Then please enter the Size for your swap. Remember, the swap size is always double from your total psychical RAM. Since mine was running under 512MB, then I’ll put 1024MB as my swap size. Click the Ok button to proceed:
6) Do follow Step 5 but select SDB for the Allowable Drives. Click Ok to continue:
7) Next is to create the partition for root. Select the Software RAID from the File System Type. Then select SDA first for the Allowable Drives. But this time, choose the Fill All Available Space option and click the Ok button:
8 ) Just follow the same step just like Step 7, but this time choose the SDB instead. Click the Ok button to complete the partitioning:
9) Upon finishing the last partitioning, the hard disk layout should looks like below. Click on the RAID button to proceed:
10) Now we will start creating the RAID device. Type /boot in the Mount Point. Select RAID1 for the RAID Level. Inside the RAID Members, please make sure you selected the right partition for the boot. From the list, just select the SDA1 and SDB1. Click Ok to create the boot partition:
11) Next is to create the RAID device for swap. Select the File System Type to Swap. Then the RAID Level is set to RAID1. Don’t forget to select the right RAID Members for the swap, which are SDA2 and SBD2. Click Ok button to save:
12) After that, now to set up the RAID device for root. Type / inside the Mount Point to indicate the root. Make sure to select the RAID Level to RAID1. By this time, the RAID Members should only left with SDA3 and SDB3, so just select both. Click Ok to complete the partitioning:
13) Below is the final screen of the partitions should looks like. If everything is correct, then press the Ok button to proceed with the installation:
14) When the installation has been completed and the server is rebooting for the first time, log into the server using the root. You can check the RAID status and progress by typing cat /proc/mdstat
15) By default, the GRUB boot loader only were installed in one of the hard disk only. If you forgot this step, your second hard disk can’t boot by itself. You need to copy the GRUB from the SDA to SDB. Just type grub and follow like below, line by line:
device (hd0) /dev/sda
root (hd0,0)
setup (hd0)
device (hd1) /dev/sdb
root (hd1,0)
setup (hd1)
16) Please take note that the software RAID will be running under MDADM. This is a software that being developed to handle the RAID procedure inside the server. You can type mdadm –help for further information
Technology
well… i wanted to update my home server to Ubuntu 9.10 from fresh but my existing install offered update… went ahead.. took 1.5 hrs and came back up perfectly fine…
its annoying… i wanted things to go wrong so that i could spend time learning doing something new…
perhaps i should clean it anyway and reinstall from scratch 🙂
Technology
useful during cleanup and found by Charanjeet Sodhi during cleanup of service data files of nagios.
find . -name ‘service-perfdata.*’ | xargs rm
Technology
Just making a note about some linux based open source products out there which provide servers to operate as routers, firewalls etc.
– Vyatta
– IPCop
– mOnOwall