Bringing up interface eth0: Device eth0 does not seem to be preset, delaying initialization – centos 6

Ajay

This normally happens when you clone the machine and boot from another hardware

Bringing up interface eth0: Device eth0 does not seem to be preset, delaying initialization.      [FAILED]

To fix this, we need to update udev’s mapping rules to point the eth0 definition to the device with the correct MAC address. Open the file /etc/udev/rules.d/70-persistent-net.rules. You should see something similar to what is below:

view source
print?
01 # This file was automatically generated by the /lib/udev/write_net_rules
02 # program, run by the persistent-net-generator.rules rules file.
03 #
04 # You can modify it, as long as you keep each rule on a single
05 # line, and change only the value of the NAME= key.
06
07 # PCI device 0x8086:0x100f (e1000) (custom name provided by external tool)
08 SUBSYSTEM==”net”, ACTION==”add”, DRIVERS==”?*”, ATTR{address}==”00:50:56:9c:00:16″, ATTR{type}==”1″, KERNEL==”eth*”, NAME=”eth0″
09
10 # PCI device 0x8086:0x100f (e1000) (custom name provided by external tool)
11 SUBSYSTEM==”net”, ACTION==”add”, DRIVERS==”?*”, ATTR{address}==”00:50:56:9c:00:18″, ATTR{type}==”1″, KERNEL==”eth*”, NAME=”eth1″

As you can see there are two PCI ethernet adapters present.

 

1 # This file was automatically generated by the /lib/udev/write_net_rules
2 # program, run by the persistent-net-generator.rules rules file.
3 #
4 # You can modify it, as long as you keep each rule on a single
5 # line, and change only the value of the NAME= key.
6
7 # PCI device 0x8086:0x100f (e1000) (custom name provided by external tool)
8 SUBSYSTEM==”net”, ACTION==”add”, DRIVERS==”?*”, ATTR{address}==”00:50:56:9c:00:18″, ATTR{type}==”1″, KERNEL==”eth*”, NAME=”eth0″

You’ll also want to update the /etc/sysconfig/network-scripts/ifcfg-eth0 file to reflect the correct MAC address. Then, after a quick system restart your eth0 adapter will be back up.

 

field separator for awk

Ajay

You can change the value of FS in the awk program with the assignment operator, `=’ (see section Assignment Expressions). Often the right time to do this is at the beginning of execution, before any input has been processed, so that the very first record will be read with the proper separator. To do this, use the special BEGIN pattern (see section BEGIN and END Special Patterns). For example, here we set the value of FS to the string “,”:

awk ‘BEGIN { FS = “,” } ; { print $2 }’

 

More generally, the value of FS may be a string containing any regular expression. Then each match in the record for the regular expression separates fields. For example, the assignment:

FS = “, \t”

FS can be set on the command line. You use the `-F’ argument to do so. For example:

awk -F, ‘program’ input-files

The value used for the argument to `-F’ is processed in exactly the same way as assignments to the built-in variable FS. This means that if the field separator contains special characters, they must be escaped appropriately. For example, to use a `\’ as the field separator, you would have to type:

# same as FS = “\\”
awk -F\\\\ ‘…’ files …

 

cron -job – examples

Ajay

1. Execute a cron job every 5 Minutes

The first field is for Minutes. If you specify * in this field, it runs every minutes. If you specify */5 in the 1st field, it runs every 5 minutes as shown below.

*/5 * * * * /home/ramesh/backup.sh

Note: In the same way, use */10 for every 10 minutes, */15 for every 15 minutes, */30 for every 30 minutes, etc.

2. Execute a cron job every 5 Hours

The second field is for hours. If you specify * in this field, it runs every hour. If you specify */5 in the 2nd field, it runs every 5 hours as shown below.

0 */5 * * * /home/ramesh/backup.sh

Note: In the same way, use */2 for every 2 hours, */3 for every 3 hours, */4 for every 4 hours, etc.

3. Execute a job every 5 Seconds

Cron job cannot be used to schedule a job in seconds interval. i.e You cannot schedule a cron job to run every 5 seconds. The alternative is to write a shell script that uses ‘sleep 5′ command in it.

Create a shell script every-5-seconds.sh using bash while loop as shown below.

$ cat every-5-seconds.sh
#!/bin/bash
while true
do
 /home/ramesh/backup.sh
 sleep 5
done

Now, execute this shell script in the background using nohup as shown below. This will keep executing the script even after you logout from your session. This will execute your backup.sh shell script every 5 seconds.

$ nohup ./every-5-seconds.sh &

4. Execute a job every 5th weekday

This example is not about scheduling “every 5 days”. But this is for scheduling “every 5th weekday”.

The 5th field is DOW (day of the week). If you specify * in this field, it runs every day. To run every Friday, specify either 5 of Fri in this field.

The following example runs the backup.sh every Friday at midnight.

0 0 * * 5 /home/ramesh/backup.sh
(or)
0 0 * * Fri /home/ramesh/backup.sh

You can either user number or the corresponding three letter acronym for the weekday as shown below.

  • 0=Sun
  • 1=Mon
  • 2=Tue
  • 3=Wed
  • 4=Thu
  • 5=Fri
  • 6=Sat

Note: Get into the habit of using Fri instead of 5. Please note that the number starts with 0 (not with 1), and 0 is for Sun (not Mon).

5. Execute a job every 5 months

There is no direct way of saying ‘every 5 months’, instead you have to specify what specific months you want to run the job. Probably you may want to run the job on 5th month (May), and 10th month (Oct).

The fourth field is for Months. If you specify * in this field, it runs every month. To run for the specific month, you have to specify the number that corresponds to the month. For example, to run the job on May and Oct, you should specify 5,10 (or) you can simply use the 3 letter acronym of the month and specify May,Oct.

The third field is for DOM (Day of the Month). If you specify * in this field, it runs every day of the month. If you specify 1 in this month, it runs 1st of the month.

The following example runs the backup.sh twice a year. i.e 1st May at midnight, and 1st Oct at midnight.

0 0 1 5,10 * /home/ramesh/backup.sh
(or)
0 0 1 May,Oct * /home/ramesh/backup.sh

Note: Don’t make the mistake of specifying 5-10 in the 4th field, which means from 5th month until 10th month. If you want only 5th and 10th month, you should use comma.

 

original post and copied from : http://www.thegeekstuff.com/2011/07/cron-every-5-minutes/

WP Twitter Auto Publish Powered By : XYZScripts.com