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Showing posts from December, 2012

Sendmail: Bypass DNS and Forward Emails to Smart Host

Scenario: We need a dumb mail server that would forward all outgoing mails (originated in the server) to a relay host/smart host. We don't want our mail server to do any DNS queries (we leave the noble task for the smart host, after all, he's "smart").
Here's how it's done in sendmail-

Create a new file in the /etc/mail directoryvim /etc/mail/service.switch ####### start of file ######### hosts files aliases files ####### end of file ###########

We add the "relay host" IP to sendmail.mcvim /etc/mail/sendmail.mc define(`SMART_HOST',`192.168.2.250')dnl ### obviously, replace the relay host address based on your requirements ### end ### m4 /etc/mail/senmdmail.mc > /etc/mail/sendmail.cf service sendmail restart NOTE: Make sure there is no dnl in the beginning of the line. The compiler will treat any starting with dnl as a comment.

And it's done. Now our mail server will not do any DNS queries and forward all outgoing mail to smart …

Password Protecting Grub

Image
To protect grub using md5 encrypted password, we can use this simple technique-


[root@zimbra ~]# grub-md5-crypt Password: Retype password: $1$zsPMx0$DkhqPFB1ouY/W7uhvCJZL1  This command generates a MD5 encrypted password that will be added to the file grub.conf. Here is my sample file-

[root@zimbra ~]# vim /etc/grub.conf ##################################################################################### default=0 timeout=5 splashimage=(hd0,0)/grub/splash.xpm.gz password --md5 $1$zsPMx0$DkhqPFB1ouY/W7uhvCJZL1 hiddenmenu title Red Hat Enterprise Linux (2.6.32-220.el6.x86_64) root (hd0,0) kernel /vmlinuz-2.6.32-220.el6.x86_64 ro root=/dev/mapper/vg_zimbra-lv_root rd_NO_LUKS rd_LVM_LV=vg_zimbra/lv_root LANG=en_US.UTF-8 rd_NO_MD quiet SYSFONT=latarcyrheb-sun16 rhgb crashkernel=auto rd_LVM_LV=vg_zimbra/lv_swap KEYBOARDTYPE=pc KEYTABLE=us rd_NO_DM initrd /initramfs-2.6.32-220.el6.x86_64.img

And we are ready. The system can be rebooted safely, and will never ask …