Setting a cron


  • administrators

    Crontab

    To display your cron file you run the following command:

    crontab -l
    

    The root user can see any users crontab file by adding :undefined:“:undefined:-u username:undefined:”:undefined:, for example:

    crontab -u rick -l 
    

    Each line is a collection of six fields separated by spaces.

    The fields are:

    • The number of minutes after the hour (0 to 59)
    • The hour in military time (24 hour) format (0 to 23)
    • The day of the month (1 to 31)
    • The month (1 to 12)
    • The day of the week(0 or 7 is Sun, or use name)
    • The command to run
    *     *     *     *     *  Command string
    -     -     -     -     -
    |     |     |     |     |
    |     |     |     |     +----- Day of week (0-7)
    |     |     |     +------- Month (1 - 12)
    |     |     +--------- Day of month (1 - 31)
    |     +----------- Hour (0 - 23)
    +------------- Min (0 - 59)
    

    The :undefined:‘:undefined:asterisks:undefined:’:undefined: are where you enter day, time ect, however they can be left as ''s , meaning null*


    To edit crontab file run:

    crontab -e
    

    To enable your preferred editor follow this quick and simple guide:force-crontab-editor-default-editor


    To list all crons in the file:

    crontab -l
    

    Example:

    Reboot the machine every hour:

    0   *   *   *   * /sbin/shutdown -r now
    

    Reboot the machine at ten minutes past midnight every day:

    10  0   *   *   * /sbin/shutdown -r now
    

    Reboot the machine every monday at 2 AM

    0   2   *   *   1  /sbin/shutdown -r now
    

    Reboot the machine using range:

    Reboot the machine within the range of hours matching 1, 2, 3 and 4AM

    *   1-4   *   *   * /sbin/shutdown -r now
    

 



  • Make ISO from DVD

    In this case I had an OS install disk which was required to be on a virtual node with no optical drive, so I needed to transfer an image to the server to create a VM

    Find out which device the DVD is:

    lsblk

    Output:

    NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT sda 8:0 0 465.8G 0 disk ├─sda1 8:1 0 1G 0 part /boot └─sda2 8:2 0 464.8G 0 part ├─centos-root 253:0 0 50G 0 lvm / ├─centos-swap 253:1 0 11.8G 0 lvm [SWAP] └─centos-home 253:2 0 403G 0 lvm /home sdb 8:16 1 14.5G 0 disk /mnt sr0 11:0 1 4.1G 0 rom /run/media/rick/CCSA_X64FRE_EN-US_DV5

    Therefore /dev/sr0 is the location , or disk to be made into an ISO

    I prefer simplicity, and sometimes deal with the fallout after the fact, however Ive repeated this countless times with success.

    dd if=/dev/sr0 of=win10.iso

    Where if=Input file and of=output file

    I chill out and do something else while the image is being copied/created, and the final output:

    8555456+0 records in 8555456+0 records out 4380393472 bytes (4.4 GB) copied, 331.937 s, 13.2 MB/s

    Fin!

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  • Recreate postrgresql database template encode to ASCII

    UPDATE pg_database SET datistemplate = FALSE WHERE datname = 'template1';

    Now we can drop it:

    DROP DATABASE template1;

    Create database from template0, with a new default encoding:

    CREATE DATABASE template1 WITH TEMPLATE = template0 ENCODING = 'UNICODE'; UPDATE pg_database SET datistemplate = TRUE WHERE datname = 'template1'; \c template1 VACUUM FREEZE;

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