Red Hat Enterprise Linux 5 Administration Unleashed

Network Troubleshooting 555Q. My system is configured to adjust the time and date for Daylights Savings Time. Ihave a cron task scheduled during the hour skipped for Daylights Savings time. Willthe cron task get executed?A. Cron is written such that any time change of less than three hours is compensatedfor by running any tasks scheduled for the missing time immediately. So, any jobsscheduled during the skipped hour is run immediately after the time change.Network TroubleshootingQ. I have an NIS server configured for my network for user authentication on all workstations.It recently had a disk failure and needed to be repaired. During the downtime,users could not log into their computers because the authentication server wasdown. Is there a way to allow users to log in when the NIS server goes down?A. If your user database doesn’t change that often, you can have a backup hard driveor hard drives ready to use should another disk failure occur. However, this solutionstill includes some downtime to change the disks. A better solution would be to setup a slave NIS server. Its user database is updated from the NIS master server, and itwill answer NIS requests should the master go down or get overloaded. Users on theworkstations will not even notice if the master NIS server goes down.Q. I have a firewall that only allows traffic on specific ports. I know that NFS uses port2049 by default, and I have not changed this. However, my NFS connections stillaren’t working. How do I allow NFS connections to my clients?A. NFS does use port 2049. It also uses several other ports, some of which are not staticby default. Refer to the “Assigning Static NFS Ports” section of Chapter 13, “NetworkFile Sharing” for details.Q. I have changed the default port of the Apache Web Server. I don’t receive any errorswhen starting the daemon, but how do I connect to the server from a web browsernow?A. If you have modified the default port number of Apache, append the IP address,hostname of the server, or the registered domain name such as www.example.comwith a colon and the port number:http://www.example.com:DQ. How do I know if my system is dropping network packets?A. If you suspect packets are being dropped during network transfers, look at output ofthe ifconfig command. The stanza for each interface contains a line for RX and aline for TX packets. Read these lines and look for the number after dropped. Ifpackets are being dropped, the number of dropped packets are listed as in thefollowing:RX packets:176430 errors:0 dropped:1567 overruns:0 frame:0TX packets:160707 errors:0 dropped:5873 overruns:0 carrier:0