Anatomy of the Linux file system: "What is a file system?
I'll start with an answer to the most basic question, the definition of a file system. A file system is an organization of data and metadata on a storage device. With a vague definition like that, you know that the code required to support this will be interesting. As I mentioned, there are many types of file systems and media. With all of this variation, you can expect that the Linux file system interface is implemented as a layered architecture, separating the user interface layer from the file system implementation from the drivers that manipulate the storage devices.
File systems as protocols
Another way to think about a file system is as a protocol. Just as network protocols (such as IP) give meaning to the streams of data traversing the Internet, file systems give meaning to the data on a particular storage medium.
Mounting
Associating a file system to a storage device in Linux is a process called mounting. The mount command is used to attach a file system to the current file system hierarchy (root). During a mount, you provide a file system type, a file system, and a mount point.
To illustrate the capabilities of the Linux file system layer (and the use of mount), create a file system in a file within the current file system. This is accomplished first by creating a file of a given size u"
Tuesday, October 14, 2008
Monday, October 13, 2008
Sort folders by size with one command
Sort folders by size with one command:
"Entire user’s data is under /home, I need to have a list of all the sub folders sorted by the size of the sub folders.
simple command to get the list of sub folders sorted by their size:
du --max-depth=1 /home/ | sort -n -r"
"Entire user’s data is under /home, I need to have a list of all the sub folders sorted by the size of the sub folders.
simple command to get the list of sub folders sorted by their size:
du --max-depth=1 /home/ | sort -n -r"
Sunday, October 12, 2008
IP Address
What's an IP address?
Every computer on a network has a unique number. On networks such as the Internet that use the TCP/IP protocol stack (which is most networks nowadays), the unique number is called an IP address. When computers on a TCP/IP network talk to each other, they address themselves by IP address.
To techies, IP addresses are 32 bit binary numbers, but to normal people they consist of four decimal numbers, each between zero and 255, separated by periods. As I write this, the IP address for the cnet.com website is 216.239.122.102. For more on IP addresses see my posting OpenDNS provides added safety for free from December of last year.
In the old days, individual computers on the Internet were directly addressable by their IP address, but now it is much more common for a router to have an IP address and for the router to act as the front man for bunch of computers on a Local Area Network.
In this scenario, the only thing that directly connects to the outside world is the router, each individual computer on the LAN goes through the router to get to the Internet. Thus, a single IP address, assigned to the router, is shared by many computers. And that means, there is no way for the outside world to identify one computer on the LAN from another. The outside world only communicates with the router.
Some people gladly share their wireless network with their neighbors. If a bad guy gets on to your wireless network and does something illegal, law enforcement may knock on your door. To the outside world, the bad guy seems to be you. All the computers on the LAN have the same public IP address, that of the router.
This brings up two points:
* Yes, law enforcement officials can trace your IP address back to your exact physical address
* What IP addresses are being used on the LAN?
To answer the second question, there are three groups of IP addresses that have been reserved for internal use only. That is, the TCP/IP rules state that these IP addresses will never be used on the public Internet. They are referred to as private IP addresses.
The most common private IP group starts with 192.168.x.x. So, for example, there can be millions of computers accessing the Internet, each using an IP address of 192.168.1.2. But, because each resides on a different Local Area Network there are no conflicts. Another group of private IP addresses starts with 10.x.x.x and the third starts with 172.x.x.x.
Your operating system deals with private IP addresses as does your router. When data moves between a Local Area Network and the Internet, the router serves as a translator between the IP addressing scheme on the inside (LAN) and the outside (Internet).* On a Windows computer, the command "ipconfig" will display the private IP address.
Every computer on a network has a unique number. On networks such as the Internet that use the TCP/IP protocol stack (which is most networks nowadays), the unique number is called an IP address. When computers on a TCP/IP network talk to each other, they address themselves by IP address.
To techies, IP addresses are 32 bit binary numbers, but to normal people they consist of four decimal numbers, each between zero and 255, separated by periods. As I write this, the IP address for the cnet.com website is 216.239.122.102. For more on IP addresses see my posting OpenDNS provides added safety for free from December of last year.
In the old days, individual computers on the Internet were directly addressable by their IP address, but now it is much more common for a router to have an IP address and for the router to act as the front man for bunch of computers on a Local Area Network.
In this scenario, the only thing that directly connects to the outside world is the router, each individual computer on the LAN goes through the router to get to the Internet. Thus, a single IP address, assigned to the router, is shared by many computers. And that means, there is no way for the outside world to identify one computer on the LAN from another. The outside world only communicates with the router.
Some people gladly share their wireless network with their neighbors. If a bad guy gets on to your wireless network and does something illegal, law enforcement may knock on your door. To the outside world, the bad guy seems to be you. All the computers on the LAN have the same public IP address, that of the router.
This brings up two points:
* Yes, law enforcement officials can trace your IP address back to your exact physical address
* What IP addresses are being used on the LAN?
To answer the second question, there are three groups of IP addresses that have been reserved for internal use only. That is, the TCP/IP rules state that these IP addresses will never be used on the public Internet. They are referred to as private IP addresses.
The most common private IP group starts with 192.168.x.x. So, for example, there can be millions of computers accessing the Internet, each using an IP address of 192.168.1.2. But, because each resides on a different Local Area Network there are no conflicts. Another group of private IP addresses starts with 10.x.x.x and the third starts with 172.x.x.x.
Your operating system deals with private IP addresses as does your router. When data moves between a Local Area Network and the Internet, the router serves as a translator between the IP addressing scheme on the inside (LAN) and the outside (Internet).* On a Windows computer, the command "ipconfig" will display the private IP address.
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