Schedule a job under Linux using cron

Posted by shands on October 22, 2010 · Leave a Comment

My last post was for a backup script that tar’ed up an entire Linux box (with the exception of some useless directories) and then uploaded it to an FTP server. Useful stuff, but a pain if you have to run it yourself manually every day! Enter, cron.

Cron is the daemon that executes commands according to a set schedule, and crontab is the utility used to manipulate it. To add a job, login as root and issue the command crontab -e. You’ll be presented with an editor for you to add the new job. The format the new line will need to format is as follows:

* * * * * command
- - - - -
| | | | |
| | | | ----- Day of week (0 - 7) (Sunday=0 or 7)
| | | ------- Month (1 - 12)
| | --------- Day of month (1 - 31)
| ----------- Hour (0 - 23)
------------- Minute (0 - 59)

So, if we wanted our backup script (located at /back/dobackup.sh) to run at 10pm every night, you’d insert:

0 22 * * * /back/dobackup.sh

Save and exit (as you’re in vi, that’s the key sequence: escape : w q enter), and it’ll be added to your crontab. To check, issue: crontab -l

Did you find this hint useful? Or are you wondering how to learn more? Well, here’s a few books that I’ve found useful over the years:

Linux Command Line and Shell Scripting Bible

Linux: The Complete Reference, Sixth Edition

Linux Pocket Guide – Essential Commands

Linux All-in-one Desk Reference

Filed under FreeBSD, Linux · Tagged with cron, crontab

Backup a Linux box through FTP (push) and tar

Posted by shands on October 22, 2010 · Leave a Comment

Another quick Linux how-to. This time how to backup up an entire box using into a tar archive and push it to an FTP server. In my case, this ran every night and the FTP server was the central tape backup unit.

It’s a good idea to create yourself a separate directory to store the backup shell script and FTP script. For want of a better name, I created /back (10 out of 10 for originality, right?). In there, first create the backup script dobackup.sh:

rm /back/*.tgz
d=$(date +%y%m%d)
tar cvpzf /back/back$d.tgz --exclude=/proc --exclude=/lost+found --exclude
    =/back --exclude=/mnt --exclude=/sys /
lftp -f /back/backftpscript

Then change the mode of the file to allow execution:

[root@nas01 /]# chmod a+x dobackup.sh

[root@nas01 /]#

And then create the second file backftpscript (the FTP script):

open -u <ftp username>,<ftp password> <ftp host>

mput /back/*.tgz

bye

That’s it – you’re good to go! Just execute /dobackup.sh and it’ll tar everything and then upload it to the specified FTP server.

Here’s an explanation as to how it works and line-by-line what’s going on:

rm /back/*.tgz

Remove last nights backup! (or traces of any others)

d=$(date +%y%m%d)

Grab todays date (in the format yymmdd) and stuff it a variable ($d)

tar cvpzf /back/back$d.tgz –exclude=/proc –exclude=/lost+found –exclude=/back –exclude=/mnt –exclude=/sys /

Create an archive, make it Verbose, Preserve the permissions, filter the archive through gZip, call the File /back/back$d.tgz (e.g back101022.tgz for 22nd Oct 2010). Exclude from the archive useless stuff like /back (the backup dir itself), /sys, /mnt, etc. And finally the target of the archive, /

lftp -f /back/backftpscript

lftp is like the ftp command, but with a lot more functionality and protocols. Probably warrants a how-to of its own, but needless to says it’s a lot more useful for use in situations like these. This particular line starts lftp and runs our ftp script, backftpscript. The contents of which are:

open -u <ftp username>,<ftp password> <ftp host>

Pretty self explanatory. Open a connection to <ftp host> and login as <ftp username> using the password <ftp password>

mput /back/*.tgz

After we’ve connected, upload (or put) all the .tgz files from our local /back directory

bye

Bid farewell and drop the connection (in a nice, polite sort of way)

Need this to run on a nightly basis? Take a look at my other how-to on cron jobs

Are you wondering how to learn more about Linux? Well, here’s a few books that I’ve found useful over the years that might just help you more:

Linux Command Line and Shell Scripting Bible

Linux: The Complete Reference, Sixth Edition

Linux Pocket Guide – Essential Commands

Linux All-in-one Desk Reference

Filed under Linux · Tagged with backup, ftp, linux, script, shell, tar

Creating and mounting an ext3 partition

Posted by shands on October 22, 2010 · Leave a Comment

It’s been a while, but here’s a quick how-to on creating a new file system and mounting on a Linux box.

My scenario was a 512MB CF card as an IDE slave – so /dev/hdb (b being the second IDE disk) – with no existing partitions, and create a mount point of /back (for backup purposes).

Here’s how:

[root@nas01 /]# fdisk /dev/hdb

Command (m for help): d

No partition is defined yet!

(Note: If you’ve got an existing partition on the drive, d will remove the partition and you’ll get a message like “Selected partition 1″. If you’ve got any additional partitions, d them too)

Command (m for help): n

Command action

e extended

p primary partition (1-4)

p

Partition number (1-4): 1

First cylinder (1-993, default 1): <hit enter>

Using default value 1

Last cylinder, +cylinders or +size{K,M,G} (1-993, default 993): <hit enter>

Using default value 993

Command (m for help): w

The partition table has been altered!

Calling ioctl() to re-read partition table.

Syncing disks.

[root@nas01 /]# mkfs.ext3 /dev/hdb1

mke2fs 1.41.8 (11-July-2009)

Filesystem label=

OS type: Linux

Block size=1024 (log=0)

Fragment size=1024 (log=0)

125488 inodes, 500440 blocks

25022 blocks (5.00%) reserved for the super user

First data block=1

Maximum filesystem blocks=67633152

62 block groups

8192 blocks per group, 8192 fragments per group

2024 inodes per group

Superblock backups stored on blocks:

8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409

Writing inode tables: done

Creating journal (8192 blocks): done

Writing superblocks and filesystem accounting information: done

This filesystem will be automatically checked every 37 mounts or

180 days, whichever comes first. Use tune2fs -c or -i to override.

[root@nas01 /]# mkdir /back

[root@nas01 /]# mount /dev/hdb1 /back

[root@nas01 /]# df -m

Filesystem 1M-blocks Used Available Use% Mounted on

/dev/hda1 1930 741 1090 41% /

tmpfs 1980 0 1980 0% /dev/shm

/dev/hdb1 474 11 439 3% /back

[root@nas01 /]#