Chapter 9 Study Guide - Revision history

Litk0013 at 00:52, 23 March 2012

2012-03-23T00:52:00Z

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	'''Scheduling commands in Linux.'''		'''Scheduling commands in Linux.'''

	at daemon (atd) – used to schedule a command to be executed one time in the future.		at daemon (atd) – used to schedule a command to be executed one time in the future.

Litk0013 at 00:51, 23 March 2012

2012-03-23T00:51:26Z

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	Schedule a job.		Schedule a job.

	at (timespec)		at (timespec) - Example: at noon or at 12:01am July 1

	at>date		at>date
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	Display a list of AT jobs:		Display a list of AT jobs:
			:*at –l
	at –l

	Display variables for Job ID:		Display variables for Job ID:
			:*at –c 1
	at –c 1

	Delete a AT job:		Delete a AT job:
			:*at –d 1
	at –d 1

	To process a script:		To process a script:
			:*at 12:01am July 4 –f /home/user1/Happy4th.sh
	at 12:01am July 4 –f /home/user1/Happy4th.sh


	Limiting access to the at daemon:		Limiting access to the at daemon:
			:*Access to scheduling at jobs can be limited with the /etc/at.allow and /etc/at.deny files.
	§ Access to scheduling at jobs can be limited with the /etc/at.allow and /etc/at.deny files.		:*If the files do not exist, only root can schedule tasks with the at daemon.
	ú If the files do not exist, only root can schedule tasks with the at daemon.		:*To allow users, create the /etc/at.allow file and add the username, one per line.
	ú To allow users, create the /etc/at.allow file and add the username, one per line.		:*To deny users, create the /etc/at.deny file. Anyone not in the file is then allowed to use the at daemon.
	ú To deny users, create the /etc/at.deny file. Anyone not in the file is then allowed to use the at daemon.
	Note: if both files exist, the system only processes the /etc/at.allow file and ignores /etc/at.deny.		Note: if both files exist, the system only processes the /etc/at.allow file and ignores /etc/at.deny.

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	The table is separated into 6 fields by a space or tab. The first five field specify the times to run the command and the sixth field is the absolute path to the command to be run.		The table is separated into 6 fields by a space or tab. The first five field specify the times to run the command and the sixth field is the absolute path to the command to be run.


	Access to scheduling at jobs can be limited with the /etc/cron.allow and /etc/cron.deny files.		Access to scheduling at jobs can be limited with the /etc/cron.allow and /etc/cron.deny files.
	§ On a newly installed Fedora system, all users have the ability to schedule tasks with cron daemon as the /etc/cron.deny contains only a single blank line.		:*On a newly installed Fedora system, all users have the ability to schedule tasks with cron daemon as the /etc/cron.deny contains only a single blank line.
	ú To allow users, create the /etc/cron.allow file and add the username, one per line. This would then limit the system compared to a clean install to only those users.		:*To allow users, create the /etc/cron.allow file and add the username, one per line. This would then limit the system compared to a clean install to only those users.
	ú To deny users, create the /etc/cron.deny file. Anyone not in the file is then allowed to use the at daemon.		:*To deny users, create the /etc/cron.deny file. Anyone not in the file is then allowed to use the at daemon.
	Note: if both files exist, the system only processes the /etc/cron.allow file and ignores /etc/cron.deny.		Note: if both files exist, the system only processes the /etc/cron.allow file and ignores /etc/cron.deny.



	To create or edit a user cron table use the –e option. The editor for crontab entries is the vi editor		To create or edit a user cron table use the –e option. The editor for crontab entries is the vi editor
	crontab –e		:*crontab –e
	Note: The crontab information is stored in the /var/spool/cron/username directory. Username is the name of the user that executed the crontab –e command.		Note: The crontab information is stored in the /var/spool/cron/username directory. Username is the name of the user that executed the crontab –e command.

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	To list the contents of your user cron table use the –l option.		To list the contents of your user cron table use the –l option.
	§ crontab –l		:*crontab –l

	To remove a cron table and all the scheduled jobs you can use the –r option.		To remove a cron table and all the scheduled jobs you can use the –r option.
	§ crontab –r		:*crontab –r

	Note: all the previous commands are specific for the user running them.		Note: all the previous commands are specific for the user running them.
	Note: root can list, edit or remove other users cron tables by using the -u option with the username.		Note: root can list, edit or remove other users cron tables by using the -u option with the username.
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	# \| \| \| \| \|		# \| \| \| \| \|
	# * * * * * command to be executed		# * * * * * command to be executed
	§ The fields are separated by a space and * indicates a wild card for all time periods.		:The fields are separated by a space and indicates a wild card for all time periods.
	§ If you want more than one consecutive day, you can specify the day range with a –(dash).		:*If you want more than one consecutive day, you can specify the day range with a –(dash).
	§ If you want more than one time period non-consecutive you can separate them by a comma.		:*If you want more than one time period non-consecutive you can separate them by a comma.
	§ If you want to specify a particular time period, every 10 min, you can specify the *(every minute) /10.		:If you want to specify a particular time period, every 10 min, you can specify the (every minute) /10.


	§ Administrative tasks that are performed on an hourly, daily, weekly or monthly basis can be scheduled simply by placing the shell script in the following directories.		Administrative tasks that are performed on an hourly, daily, weekly or monthly basis can be scheduled simply by placing the shell script in the following directories.
	ú Scripts to be executed hourly - /etc/cron.hourly directory.		:*Scripts to be executed hourly - /etc/cron.hourly directory.
	ú Scripts to be executed daily - /etc/cron.daily directory.		:*Scripts to be executed daily - /etc/cron.daily directory.
	ú Scripts to be executed weekly - /etc/cron.weekly directory.		:*Scripts to be executed weekly - /etc/cron.weekly directory.
	ú Scripts to be executed monthly - /etc/cron.monthly directory.		:*Scripts to be executed monthly - /etc/cron.monthly directory.
	§ The cron daemon runs the /etc/cron.d/Øhourly script which executes the files in the directory /etc/cron.hourly one minute past the hour, every hour.		The cron daemon runs the /etc/cron.d/Øhourly script which executes the files in the directory /etc/cron.hourly one minute past the hour, every hour.
	§ For troubleshooting purposes: The /etc/cron.hourly/Øanacron file starts the anacron daemon which then executes the contents of the /etc/cron.daily, /etc/cron.weekly, and the /etc/cron.monthly directories at the times specified in the /etc/anacrontab file.		For troubleshooting purposes: The /etc/cron.hourly/Øanacron file starts the anacron daemon which then executes the contents of the /etc/cron.daily, /etc/cron.weekly, and the /etc/cron.monthly directories at the times specified in the /etc/anacrontab file.

Nguy0837 at 00:38, 23 March 2012

2012-03-23T00:38:06Z

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	:*ps –f displays a full list of information about each process, including the UID, PID, PPID, CPU utilization, start time, terminal, processor time, and command name		:*ps –f displays a full list of information about each process, including the UID, PID, PPID, CPU utilization, start time, terminal, processor time, and command name
	:*ps –l displays a long list of information about each process, including the flag, state, UID, PID, PPID, CPU utilization, priority, nice value, address, size, WCHAN, terminal, and command name		:*ps –l displays a long list of information about each process, including the flag, state, UID, PID, PPID, CPU utilization, priority, nice value, address, size, WCHAN, terminal, and command name
	~~Example:[root@server1 ~]# ps –l~~

	~~F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD~~
	~~4 S 0 2159 2156 0 80 0 - 1238 wait tty2 00:00:00 bash~~

	:*ps –a displays all processes running on terminals		:*ps –a displays all processes running on terminals
	:*ps –x displays all processes that do not run on terminals		:*ps –x displays all processes that do not run on terminals

Nguy0837 at 00:37, 23 March 2012

2012-03-23T00:37:33Z

← Older revision		Revision as of 00:37, 23 March 2012
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	F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD		F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
	4 S 0 2159 2156 0 80 0 - 1238 wait tty2 00:00:00 bash		4 S 0 2159 2156 0 80 0 - 1238 wait tty2 00:00:00 bash


	:*ps –a displays all processes running on terminals		:*ps –a displays all processes running on terminals

Nguy0837 at 00:37, 23 March 2012

2012-03-23T00:37:09Z

← Older revision		Revision as of 00:37, 23 March 2012
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	Example:[root@server1 ~]# ps –l		Example:[root@server1 ~]# ps –l

	F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD		F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
	4 S 0 2159 2156 0 80 0 - 1238 wait tty2 00:00:00 bash		4 S 0 2159 2156 0 80 0 - 1238 wait tty2 00:00:00 bash

Nguy0837 at 00:36, 23 March 2012

2012-03-23T00:36:41Z

← Older revision		Revision as of 00:36, 23 March 2012
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	:*ps –l displays a long list of information about each process, including the flag, state, UID, PID, PPID, CPU utilization, priority, nice value, address, size, WCHAN, terminal, and command name		:*ps –l displays a long list of information about each process, including the flag, state, UID, PID, PPID, CPU utilization, priority, nice value, address, size, WCHAN, terminal, and command name
	Example:[root@server1 ~]# ps –l		Example:[root@server1 ~]# ps –l

	F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD		F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
	4 S 0 2159 2156 0 80 0 - 1238 wait tty2 00:00:00 bash		4 S 0 2159 2156 0 80 0 - 1238 wait tty2 00:00:00 bash

Nguy0837 at 00:36, 23 March 2012

2012-03-23T00:36:21Z

← Older revision		Revision as of 00:36, 23 March 2012
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	:*ps –l displays a long list of information about each process, including the flag, state, UID, PID, PPID, CPU utilization, priority, nice value, address, size, WCHAN, terminal, and command name		:*ps –l displays a long list of information about each process, including the flag, state, UID, PID, PPID, CPU utilization, priority, nice value, address, size, WCHAN, terminal, and command name
	Example:[root@server1 ~]# ps –l		Example:[root@server1 ~]# ps –l
			F S UID PID PPID C PRI NI ADDR SZ WCHAN TTY TIME CMD
			4 S 0 2159 2156 0 80 0 - 1238 wait tty2 00:00:00 bash

Nguy0837 at 00:33, 23 March 2012

2012-03-23T00:33:35Z

← Older revision		Revision as of 00:33, 23 March 2012
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	:*ps –f displays a full list of information about each process, including the UID, PID, PPID, CPU utilization, start time, terminal, processor time, and command name		:*ps –f displays a full list of information about each process, including the UID, PID, PPID, CPU utilization, start time, terminal, processor time, and command name
	:*ps –l displays a long list of information about each process, including the flag, state, UID, PID, PPID, CPU utilization, priority, nice value, address, size, WCHAN, terminal, and command name		:*ps –l displays a long list of information about each process, including the flag, state, UID, PID, PPID, CPU utilization, priority, nice value, address, size, WCHAN, terminal, and command name
			Example:[root@server1 ~]# ps –l


	:*ps –a displays all processes running on terminals		:*ps –a displays all processes running on terminals
	:*ps –x displays all processes that do not run on terminals		:*ps –x displays all processes that do not run on terminals

Nguy0837 at 00:27, 23 March 2012

2012-03-23T00:27:34Z

← Older revision		Revision as of 00:27, 23 March 2012
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	:*kill –l displays different kill signal names		:*kill –l displays different kill signal names
	Example:[root@server1 ~]# kill -l		Example:[root@server1 ~]# kill -l

	1)SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL		1)SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL
	5)SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE		5)SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE

Nguy0837 at 00:27, 23 March 2012

2012-03-23T00:27:15Z

← Older revision		Revision as of 00:27, 23 March 2012
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	:*kill send to kill signals		:*kill send to kill signals
	:*kill –l displays different kill signal names		:*kill –l displays different kill signal names
			Example:[root@server1 ~]# kill -l
	1)SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL		1)SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL
	5)SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE		5)SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE