Add following code in “/etc/inittab” file to secure it from change in single user mode:
# password protect single user mode
su:S:wait:/sbin/sulogin
References:
http://thedaneshproject.com/posts/password-protect-single-user-mode/
Thursday, May 27, 2010
Tuesday, May 11, 2010
Memory Management
In Memory management, virtual memory is highly used concept.
Generally Virtual memory is per process but not for whole system. Pagetables, Translation lookaside buffers etc are swapped when a context switching of process happens.
In Linux:
Approximately the first two megabytes of physical memory are reserved
– For the PC architecture and for OS text and data, the rest is available for paging
• The logical address space of a process is divided into two parts
– 0x00000000 to PAGE_OFFSET-1 can be addressed in either
user or kernel mode
– PAGE_OFFSET to 0xffffffff can be addressed only in
kernel mode
– PAGE_OFFSET is usually 0xc00000000
Generally Virtual memory is per process but not for whole system. Pagetables, Translation lookaside buffers etc are swapped when a context switching of process happens.
In Linux:
Approximately the first two megabytes of physical memory are reserved
– For the PC architecture and for OS text and data, the rest is available for paging
• The logical address space of a process is divided into two parts
– 0x00000000 to PAGE_OFFSET-1 can be addressed in either
user or kernel mode
– PAGE_OFFSET to 0xffffffff can be addressed only in
kernel mode
– PAGE_OFFSET is usually 0xc00000000
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