Operating Systems - Linux, Aix, Solaris, Hpux, Win

Write Through & Write Back Caches
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Write Through mode (Write Through Cache)

Data is written to both the cache and the drive. Also for read operations, it supplies a faster access to the data, as it s in the cache.

This method adds some time to the Write operations, as data is need to be written to disk+cache.

Write Back mode (Write Back Cache)

In this mode/method, data is initially written to cache.. Data is written to disk only When required. This improves write performance.

But there is a risk in this method, as if the data in the cache is lost before its written to disk, data in the cache will be lost, and cant be recovered.

Endian Formats For different platforms:

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PLATFORM_ID PLATFORM_NAME  ENDIAN_FORMAT
----------- -------------------------------- --------------
          1 Solaris[tm] OE (32-bit)          Big
          2 Solaris[tm] OE (64-bit)          Big
          7 Microsoft Windows IA (32-bit)    Little
         10 Linux IA (32-bit)                Little
          6 AIX-Based Systems (64-bit)       Big
          3 HP-UX (64-bit)                   Big
          5 HP Tru64 UNIX                    Little
          4 HP-UX IA (64-bit)                Big
         11 Linux IA (64-bit)                Little
         15 HP Open VMS                      Little
          8 Microsoft Windows IA (64-bit)    Little
          9 IBM zSeries Based Linux          Big
         13 Linux 64-bit for AMD             Little
         16 Apple Mac OS                     Big
         12 Microsoft Windows 64-bit for AMD Little
         17 Solaris Operating System (x86) Little


Linux Remount Command:
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remount

Attempt to remount an already-mounted filesystem. This is commonly used to change the mount flags for a filesystem, especially to make a readonly filesystem writeable. It does not change device or mount point.The remount functionality follows the standard way how the mount command works with options from fstab. It means the mount command doesn't read fstab (or mtab) only when a device and dir are fully specified. mount -o remount,rw /dev/foo /dir

Unix Signals:

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Name     Num   Action    Description

       0          0   n/a       exit code indicates signal may be sent

       ALRM      14   exit

       HUP        1   exit

       INT        2   exit

       KILL       9   exit      cannot be blocked

       PIPE      13   exit

       POLL           exit

       PROF           exit

       TERM      15   exit

       USR1           exit

       USR2           exit

       VTALRM         exit

       STKFLT         exit      might not be implemented

       PWR            ignore    might exit on some systems

       WINCH          ignore

       CHLD           ignore

       URG            ignore

       TSTP           stop      might interact with the shell

       TTIN           stop      might interact with the shell

       TTOU           stop      might interact with the shell

       STOP           stop      cannot be blocked

       CONT           restart   continue if stopped, otherwise ignore

       ABRT       6   core

       FPE        8   core

       ILL        4   core

       QUIT       3   core

       SEGV      11   core

       TRAP       5   core

       SYS            core      might not be implemented

       EMT            core      might not be implemented

       BUS            core      core dump might fail

       XCPU           core      core dump might fail

       XFSZ           core      core dump might fail

Export and Mount Nfs shares (Linux to Linux)

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On the target (where you want to share your filesystem), take the following actions;

• Open /etc/exports file

                    vi /etc/exports

• Add the directory you want to share with *, read write and sync options..

                  /directory_shared *(rw,sync)

• Restart the Nfs service

                /etc/init.d/nfs restart , or service nfs restart

On the target , take the following actions;

• Create hte directory where you want to mount the exported nfs.

              mkdir /mnt/nfs

• Mount the nfs share using the following

              mount -t nfs4 nfsserver-name-or-ip:/directory_shared /mnt/nfs
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