Timed tasks (Crond in Linux)

Scheduled Tasks

1. Timing Task Basics

Writing format: Time-sharing week /bin/bash xxx.sh >/dev/null 2>&1 (or write to a file, if not, each scheduled task execution will generate a message to root, resulting in inode Full of problems). (Open mail Service will accumulate to mailboxfile/var/spool/mail/root(the time will be divided)If the mailbox is not opened, it will accumulate in the mailboxin this directory (/var/spool/postfix/maildrop)(all small files)

Illustrations:

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1. Common commands (and files)

crontab-l # Viewing scheduled tasks that have been set

crontab-r # empty all Scheduled Tasks

crontab-e # Write timed tasks (essentially writing this file /var/spool/cron/root)

# The system itself is timed tasks such as log splitting, configuration file /etc/crontab system poisoning after virus easy to write timed tasks here again

2. Dependent programs

crond # Note the difference between commands, easy to mix. (sshd,network is the daemon, need to start the program)

/sbin/service crond Start    // start service
/sbin/service Crond Stop  // Close service
/sbin/service crond Restart  //Restart service
/sbin/service Crond Reload   // reload configuration
/sbin/service crond Status  // View service status

3. Standard writing format for timed tasks

A. now the command line test is feasible

B. put in script (absolute path required)

C. writing timed tasks ( tab Key not supported) (default no EXECUTE permission)

D. Check the timing task execution log and script effect to confirm normal execution. (/var/logl/cron)

write a few big mistakes:

A. timed tasks Multi-use script completion, if the command is written,the date +%f % has special meaning need \ swivel chair.

B. scripting timed task after fixed format >/dev/null 2>&1 (> file, only one exists)

C. Most environment variables are not recognized, so absolute path writing

D. package directory, to switch to the current directory, and then use a relative path does not error.

VI shortcut key? Improve the speed of writing, Master must!

:Wq

:q! # save, use every day, must be

G last line

GG on the front side

100gg to a specified line # large, jump lines

0 ^ Fast to the beginning of the line

$ Fast to end of line

o create a new line at the cursor position and go into input mode

O Previous Line

DD Delete cursor line (cut) # DG cut cursor to last line

P Paste (no need to go to input mode) # 100p paste

YY copy cursor current line # jump at one line level

U undo the previous action

/3306 Search content n continue search next n search # search function

v im- specific Properties

VI or vim shutdown unexpectedly, power off, disconnect, in the open file will be error. There is a . XXXX.SWP;E, ignoring the power outage, did not save the file, re-open the original file;R Recovery was not saved just now.

After the last line of colons R--- enter ---:wq---(view the original file, has been restored, and then open will repeat the error, delete hidden files can be)

E still error, also need to delete temporary files

D Delete both the temporary file and the local delete both can

2. Enterprise Applications

interview questions: Every night to pack the Web program, and the date of the command to back up files. (Packaged ACHF can be packaged with soft links)

Answer:

VI web_back.sh

! #/bin/bash

/bin/tar ZCHF web_backup$ (date +%f). tar.gz./www

Crontab-e

XX * * * */bin/bash/xxx/web_back.sh >/dev/null 2>&1

Analysis: The work of the scheduled tasks are usually early morning execution ~

This article is from the "Do Something Serious" blog, please keep this source http://edencheng.blog.51cto.com/12260487/1971495

Timed tasks (Crond in Linux)