Rescue mode:

Rescue mode provides the ability to boot a small Red Hat Enterprise Linux environment entirely from CD-ROM, or some other boot method, instead of the system’s hard drive. As the name implies, rescue mode is provided to rescue you from something. During normal operation, your Red Hat Enterprise Linux system uses files located on your system’s hard drive to do everything — run programs, store your files, and more.

Emergency Mode:

In emergency mode, you are booted into the most minimal environment possible. The root file system is mounted read-only and almost nothing is set up. The main advantage of emergency mode over single-user mode is that the init files are not loaded. If init is corrupted or not working, you can still mount file systems to recover data that could be lost during a re-installation.

Single-User mode:

In single-user mode, your computer boots to runlevel 1. Your local file systems are mounted, but your network is not activated. You have a usable system maintenance shell. Unlike rescue mode, single-user mode automatically tries to mount your file system. Do not use single-user mode if your file system cannot be mounted successfully. You cannot use single-user mode if the runlevel 1 configuration on your system is corrupted.

His first entry lays the foundation of the basis of the x86 Intel chipset, memory map, and logical motherboard layout. This provides a basic understanding about the traditional hardware motherboard implementations.

Next, he describes BIOS initialization, and loading of the MBR. This briefly touches on the boot loader which starts the Linux bootstrap phase.

Finally, the kernel boot process is detailed with links to C and Assembly source code, with a brief narrative of exactly what is happening.

This was an awesome description of the early-on start up and initialization phases of hardware and bootstrapping of the O/S. Gustavo provides a great description of real-mode and protected-mode CPU states.

Attaching to process 2575Reading symbols from /usr/sbin/gpm...(no debugging symbols found)...done.
Using host libthread_db library "/lib/tls/libthread_db.so.1".Reading symbols from /lib/tls/libm.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib/tls/libm.so.6Reading symbols from /lib/tls/libc.so.6...(no debugging symbols found)...done.
Loaded symbols for /lib/tls/libc.so.6Reading symbols from /lib/ld-linux.so.2...(no debugging symbols found)...done.
Loaded symbols for /lib/ld-linux.so.2

0x0046e7a2 in _dl_sysinfo_int80 () from /lib/ld-linux.so.2

(gdb) generate-core-fileSaved corefile core.2575

(gdb) detachDetaching from program: /usr/sbin/gpm, process 2575

(gdb) quit

$ ls -al core.*-rw-r--r--  1 root root 2468288 Dec 11 13:49 core.2575

voidsendrequest(const char *cmd, char *local, char *remote, int printnames){  volatile long bytes = 0

while ((c = read(fileno(fin), buf, sizeof (buf))) > 0) {     printf("Bytes (%ld) is incremented by %d\n", bytes, c);
bytes += c;     for (bufp = buf; c > 0; c -= d, bufp += d)
if ((d = write(fileno(dout), bufp, c)) <= 0)
break;   ......}

GROUP        DISK         DEVICE       TAG          OFFSET    LENGTH    FLAGS
oradg        c3t20d1      c3t20d1s2    c3t20d1      104848640 1536      -
oradg        c3t20d3      c3t20d3s2    c3t20d3      104848640 1536      -
oradg        c3t20d5      c3t20d5s2    c3t20d5      104848640 1536      -
oradg        c3t20d7      c3t20d7s2    c3t20d7      104848640 1536      -
oradg        c3t20d9      c3t20d9s2    c3t20d9      104848640 1536      -