Developers in my office constantly complain that the SMTP server is down and no mails are being sent out. We come back saying that their application is buggy. Most often after hours of troubleshooting the problem will turn out to be the application itself.

Here’s a simple way to test your SMTP server over port 25 using Telnet to proof them wrong.

Telnet to the server via port 25.

1. Key in “EHLO example.com” and hit enter.

2. Key in “MAIL FROM: sender@domain.com” and hit enter.

3. Key in “RCPT TO: recipient@domain.com” and hit enter.

4. Key in “DATA” and hit enter.

5. Key in your message body and hit enter.

6. Key in ” . ” and press enter.

If you received the mail then your SMTP is working fine.

Sample output,
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Another issue that popped up tonight. The time on a payroll server seem to be slower then usual. Futher troubleshooting on the box revealed that it took 4 seconds to move 1 second on the server. This caused the payroll servers to stop communicating between each other as time sync was part of a security measure built into the payroll software we run here.

Some googling later it seem to be a BUG with the kernel. The fix, suggested to either update the kernel, recompile the kernel or add some kernel parameters in GRUB to fix the issue. I decided to go with the kernel parameters because this was a production server and the downtime window was very slim.

The fix,

1. vi /etc/boot/grub.conf
2. Add to the end of the kernel line. “clock=pit noapic nolapic”
3. reboot and check time. “watch date”

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We had a DC shutdown last night, been in the office for almost 20 hours now. I’m sleepy,tired,sticky,red eyed and the damn 10 year old RS6000 box running AIX 4.3 decided to stay down.

The box was trying to connect to a NFS share on the network before the network services came up. This cause the RS6000 to stall at boot up.

The fix the below fixed the problem.

1. Restart the machine.
2. Wait the the AIX splash screen to come up. Devices begin to initialize here.
3. When you see the [keyboard] word on screen hit the F5 button or the 5 key depending on your console.
4. Choose “single user mode” when the maintenance screen comes up.
5. Edit the /etc/filesystems file and remove the NFS entries.
6. Reboot.

Hitting F1 or the 1 key will take you to the SMS (System Management Services) menu where you can access system configurations liek the network settings, boot sequence, firmware update and others….

Source: Sys Admin Pocket Survival Guide