An application can register an event into a file as a result of an error, warning, etc., and at that moment, it may be interesting to restart the involved service or for instance, to send an email reporting the alarm, all automatically.
Here is where swatch turns up. You have got two ways to install it: either by means of the package which each distribution keeps in its repositories or directly by compiling the source code.
In the case of Ubuntu, the installation is really simple: aptitude install swatch. But in RHEL or CentOS, the package is not available in the official repositories of such distributions.
Therefore, in the present article I am going to develop the installation of swatch (3.2.3) on CentOS 6.0 (32 bits, minimal installation) by downloading and installing the suitable packages from RPM PBone Search.
[root@centos tmp]# rpm -i perl-Carp-Clan-6.03-2.el6.noarch.rpm [root@centos tmp]# rpm -i perl-Bit-Vector-7.1-2.el6.i686.rpm [root@centos tmp]# rpm -i perl-Date-Calc-6.3-2.el6.noarch.rpm [root@centos tmp]# rpm -i perl-Date-Manip-5.54-4.el6.noarch.rpm [root@centos tmp]# rpm -i perl-TimeDate-1.16-11.1.el6.noarch.rpm [root@centos tmp]# rpm -i perl-Time-HiRes-1.9721-115.el6.i686.rpm [root@centos tmp]# rpm -i perl-File-Tail-0.99.3-8.el6.noarch.rpm [root@centos tmp]# rpm -i perl-Mail-Sendmail-0.79-12.el6.noarch.rpm [root@centos tmp]# rpm -i swatch-3.2.3-2.el6.noarch.rpm
So that swatch can send alarms by email, you have to install some kind of MTA (Mail Transfer Agent) on your system, such as Postfix.
[root@centos ~]# yum install postfix [root@centos ~]# cat /etc/postfix/main.cf ... # Internet hostname myhostname = centos.local # Local Internet domain name mydomain = local # Domain that locally-posted mail appears to come from myorigin = $myhostname # Network interface addresses to receive mail inet_interfaces = all # List of domains to consider itself the final destination mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain ... [root@centos ~]# service postfix restart [root@centos ~]# chkconfig postfix on
Through the following example, we will control the /var/log/secure file in order to detect the login of the user javi (we must look for the string "Accepted password for javi").
First of all, we have to create a directory to drop off the configuration files of swatch. Afterwards, we must set up a file with the needed instructions to log the access for the user javi.
[root@centos ~]# mkdir /etc/swatch [root@centos ~]# cat /etc/swatch/swatch.conf watchfor /Accepted password for javi/ mail addresses=root\@centos.local,subject="Session opened by javi"
With the previous line, swatch will monitor the content of a concrete file which will be later given with the target of matching the requested string. When the coincidental text is found, an email will be passed down.
So as to start swatch, we must run the next command ('-t' option comes from the traditional 'tail -f'). If instead of using '-t' parameter, you add '-f', swatch would execute the defined configuration once and then, close the file. In this manner, the file is not open as in the case of a typical 'tail -f'.
[root@centos ~]# swatch -c /etc/swatch/swatch.conf -t /var/log/secure
Swatch has got other many options for its configuration file, such as outputting the matched pattern, sending a bell, executing commands and so on. The following example watches for a couple of strings.
[root@centos ~]# cat /etc/swatch/swatch.conf watchfor /Accepted password for javi|Accepted password for pepe/ echo=red