Linux

Corporate Firewall - SSH and port 443 goodness

Things you’ll need; (basic instructions) SSH - either Linux or Open SSH for windows (set this up first and ensure its working!). I have only used Linux, so i do not know the details of setting up a Open SSH box on windows (good luck).

Router with pinhole or port forwarding abilities. – forward your external 443 port to internal 22 on your SSH box

Putty.exe - use this to test your SSH connection locally (you should be able to connect on port 22 locally or 443 externally)

Linux - Installing VirtualBox additions

The following works on CentOs / Fedora / redhat etc… 

Logon to your distro. The packages you need are the kernel-devel.i686, kernel.i686 (if not the latest), and gcc.i386 (complier)

yum -y install kernel.i686 gcc.i386

reboot as the kernel needs to load, then logon again install the kernel dev; 

yum -y install kernel-devel.i686

Now you want to present the virtualbox additions to the cdrom drive on your distro. Click “install additions” on the virtualbox guest console. 

VMware Server 2.0 - Infrastructure Client

One thing i like about vmware server 2.0, is that you are not forced to use the web console in all cases.

If you are lucky enough to have access to VMware Infrastructure Client 2.5 you can connect via it using the following syntax at the logon screen;

IP address / Name : http://192.168.9.100

If you enter a URL in the host field, use your root and correct password you should be able to logon without issue. Welcome to a nice fast GUI admin console.

Linux - crontab

Time to schedule some tasks!

First you need to make sure your in the /etc/cron.d/cron.allow file. If you are not SU to root and add yourself into it.

Now to create your new crontab file;

crontab -e

You are in vi in your newly created crontab file (note if you do not have access to do this it will say so)

Now, i’m no expert at using vi, but if you press i you will go into insert mode. Do this, then type the cron job details. A typical cron job will look like this

Linux - Hard Drive Performance

Or lack of.

You must insure that your drives are using the sata driver (if they are sata disks), quickest way to check is that they will be called sda sdb etc…. and not hda hdb, as this is the default IDE driver and will slow down the performance majorly.

How to check performance;

hdparm -tT /dev/hda

Modern drives should be getting over 50MB/s easily. If your getting about 5MB/s you have the problem.

Linux - mapping to a windows share (SMB)

As per below. First you will need to install samba client.

In Fedora / Centos …

yum -y samba-client

then use the mount command to mount the share to a directory… 

mount -t cifs -n //192.168.9.70/software /mnt/sharename -o username=guest,password=

It will be similar in other distros. Remember to create the /mnt/sharename directory before trying to mount any share to the directory. Directories are created like so;

mkdir /mnt/sharename

Linux - setting the time

How to set the time in Linux; (from a command line)

date -s “09/21/2007 09:20:00”

hwclock –systohc

the second command links the time back to the hardware clock.

Note: within a vm guest it is always advised to install the guest additions as the time on a guest can slowly move away from the correct time.

VMWare Performance tips

these are tested from experience…. (the following is true on vmware server 1.0.6 on a linux host)

  • Always use only 1 Virtual CPU - i have found that most times even if you have heaps of cores to spare on the host, a single virtual core is faster.
  • Set the memory to the recommended level when possible - 256Mb sounds shit when you have 4gb, doesn’t matter - set it to 256Mb (increase only if excessive paging on the guest). Let linux and vmware manage the memory, in most cases it does a much better job than windows. Do not disable memory page trimming on any of the guests, this gives more memory back to the host to cache other more important activity (disk etc)
  • Never use 2gb split files for the virtual disk unless you have to transfer the vm onto a file system that doesn’t support larger files.
  • Load the latest drivers for your NIC on the host
  • Be nice to your physical disk - do not load all your VM’s on a single drive - the HDD is the slowest part of the system, dont saturate it. I use either a raid 0 running multiple vm’s (with backups) or dedicated drives per set of vm’s. This excludes enterprise level raids which can handle much higher level of simultaneous requests.
  • Install vmware tools on all guest machines

watch your pings - ping your guests… they should never loose a ping. If they do you are loading the cpu to high and the host cannot process the network queries. As above use only one virtual cpu. Also ensure you have the latest network driver loaded for your NIC on the host.