mysqldump & gzip commands to properly create a compressed file of a MySQL database using crontab

Question

I am having problems with getting a crontab to work. I want to automate a MySQL database backup.

The setup:

• Debian GNU/Linux 7.3 (wheezy)
• MySQL Server version: 5.5.33-0+wheezy1(Debian)
• directories user, backup and backup2 have 755 permission
• The user names for MySQL db and Debian account are the same

From the shell this command works

mysqldump -u user -p[user_password] [database_name] | gzip > dumpfilename.sql.gz

When I place this in a crontab using crontab -e

* * /usr/bin/mysqldump -u user -pupasswd mydatabase | gzip> /home/user/backup/mydatabase-backup-`date +\%m\%d_\%Y`.sql.gz >/dev/null 2>&1

A file is created every minute in /home/user/backup directory, but has 0 bytes.

However when I redirect this output to a second directory, backup2, I note that the proper mysqldumpfile duly compressed is created in it. I am unable to figure what is the mistake that I am making that results in a 0 byte file in the first directory and the expected output in the second directory.

* * /usr/bin/mysqldump -u user -pupasswd my-database | gzip> /home/user/backup/mydatabase-backup-`date +\%m\%d_\%Y`.sql.gz >/home/user/backup2/mydatabase-backup-`date +\%m\%d_\%Y`.sql.gz 2>&1

I would greatly appreciate an explanation.

Thanks

Answer 1

First the mysqldump command is executed and the output generated is redirected using the pipe. The pipe is sending the standard output into the gzip command as standard input. Following the filename.gz, is the output redirection operator (>) which is going to continue redirecting the data until the last filename, which is where the data will be saved.

For example, this command will dump the database and run it through gzip and the data will finally land in three.gz

mysqldump -u user -pupasswd my-database | gzip > one.gz > two.gz > three.gz

$> ls -l
-rw-r--r--  1 uname  grp     0 Mar  9 00:37 one.gz
-rw-r--r--  1 uname  grp  1246 Mar  9 00:37 three.gz
-rw-r--r--  1 uname  grp     0 Mar  9 00:37 two.gz

My original answer is an example of redirecting the database dump to many compressed files (without double compressing). (Since I scanned the question and seriously missed - sorry about that)

This is an example of recompressing files:

mysqldump -u user -pupasswd my-database | gzip -c > one.gz; gzip -c one.gz > two.gz; gzip -c two.gz > three.gz

$> ls -l
-rw-r--r--  1 uname  grp  1246 Mar  9 00:44 one.gz
-rw-r--r--  1 uname  grp  1306 Mar  9 00:44 three.gz
-rw-r--r--  1 uname  grp  1276 Mar  9 00:44 two.gz

This is a good resource explaining I/O redirection: http://www.codecoffee.com/tipsforlinux/articles2/042.html