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Showing posts from November, 2017

Linux Filesystem  Permissions Most simplified

FilesystemPermissions
Permission On File On directory



Read

View file contents List directory contents (ls)
Write

Alter file contents Alter directory contents (delete files, create files)
Execute

Run an executable file Make it the current directory (cd to it



Numeric codes follow octal notation
usergroupother 4 2 14 2 14 2 1 r w xr w xr w x
For example, rwxr—--x becomes 741

Linux Boot Play-byPlay: Theory Of Operation

The PC-Router boot process is based (like all LRP boot processes) on the Intel x86 method of booting.The process is described below using syslinux as the boot loader:




1.Your BIOS determines what device is the boot device (CD-ROM drive, Floppy, hard disk)
2.Your BIOS finds track 0, sector 1 at physical address 0x7C00
3.BIOS blindly loads the first sector (512 bytes) into memory at 0x9000.The first sector could be one of the following things:
a. the raw Linux bootsector - the linux kernel has a tiny piece of assembler code at it’s head that knows how to make the BIOS calls to hardware to load the rest of the kernel and decompress itself.The raw Linux bootsector must, obviously, be where the BIOS wants to find the bootsector: track 0, sector 1, phys addr 0x7C00.
b. another bootsector - a tiny piece of code that provides a choice of which Linux kernel (if more than one exists) to start, knows where on the disk that Linux kernel is and provides for sending options to the kernel at boot time.
Whe…