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Full Discussion: about fsck
Top Forums UNIX for Dummies Questions & Answers about fsck Post 302324580 by vbe on Thursday 11th of June 2009 06:58:11 AM
Old 06-11-2009
The secret of UNIX's speed is its buffers... and the main reason you must NEVER turn off a UNIX system by power off - It needs a clean shutdown in order to flush the buffers write to disk any pending write and unmount cleanly all file sytems in order to set the "clean" flag for next reboot...
Total buffer size depends on the system but can reach the GB 400-600 MB is common...

And so after a crash or dirty shutdown, it can take ages at next reboot for the system to come up (yes hours... in fsck...). And then came JFS - what a relief..
There are good books on the subject you know...
To make it simple : See JFS (like VXFS) as a database (oracle?), in case of crash it knows how to recover and if cant totally, will drop the last transaction in order to be in a coherent state...
 

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halt(1M)						  System Administration Commands						  halt(1M)

NAME
halt, poweroff - stop the processor SYNOPSIS
/usr/sbin/halt [-dlnqy] /usr/sbin/poweroff [-dlnqy] DESCRIPTION
The halt and poweroff utilities write any pending information to the disks and then stop the processor. The poweroff utility has the machine remove power, if possible. The halt and poweroff utilities normally log the system shutdown to the system log daemon, syslogd(1M), and place a shutdown record in the login accounting file /var/adm/wtmpx. These actions are inhibited if the -n or -q options are present. OPTIONS
The following options are supported: -d Force a system crash dump before rebooting. See dumpadm(1M) for information on configuring system crash dumps. -l Suppress sending a message to the system log daemon, syslogd(1M), about who executed halt. -n Prevent the sync(1M) before stopping. -q Quick halt. No graceful shutdown is attempted. -y Halt the system, even from a dialup terminal. FILES
/var/adm/wtmpx History of user access and administration information. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO
dumpadm(1M), init(1M), reboot(1M), shutdown(1M), sync(1M), syslogd(1M), inittab(4), attributes(5), smf(5) NOTES
The halt and poweroff utilities do not cleanly shutdown smf(5) services. Execute the scripts in /etc/rcnum.d or execute shutdown actions in inittab(4). To ensure a complete shutdown of system services, use shutdown(1M) or init(1M) to reboot a Solaris system. SunOS 5.11 2 Nov 2004 halt(1M)
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