Eric Stewart: Running Off At The Mouth

Tag: centos

NTP, ntpd, ntpq, and The Perils Of “Time”

by on Aug.06, 2015, under Computers, Networking, Technology

We ran into a “time” situation at work, and I learned quite a bit about how NTPD works, and what exactly all the information in ntpq means. This has to do with the “Leap Second” that was instituted on June 30, 2015.




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Nagios’s check_ntp_peer, IPv6, and ntp.conf

by on Jun.03, 2014, under Networking, Technology

As is not unusual, I run into an edge case that might be specific to us. While attempting to monitor IPv6 reachability of an NTP server I had just upgraded, I ran into an interesting case where NTP was responding via IPv4, but not IPv6, and they appeared to be identically configured.







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Restarting iptables and MySQL slave connections

by on Feb.27, 2014, under Networking, Technology

It’s been a while since I’ve done more than just update the Unified Trees post for new versions, and I stumbled across an issue that Linux administrators that make use of iptables should be aware of. The case is actually true for any “client initiated connection” when it comes to iptables – not just MySQL slaves. That’s just where I stumbled across the issue.







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Packet Captures and Offloaded Functions

by on Sep.05, 2013, under Networking, Technology

A fellow engineer attempting to debug a jumbo frames issue was seeing what should have been a bunch of fragmented frames as a single 13,000 byte frame. Once he figured out why, I was told to fix it. Here’s my solution.







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xinetd (tftpd), the “bind” option, and clustering

by on Jul.11, 2013, under Computers, Networking, Technology

Just a quickie, probably subject to some editing later on, about how to use the “bind” option multiple times with a given service – mainly, to have a TFTP server operate from behind a virtual IP as the virtual IP (instead of becoming its real IP in the middle of the transfer).







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CentOS: Renaming Network Interfaces

by on Jan.30, 2013, under Networking, Technology

Just a quickie post about something that was requested of me by the other engineers. You can rename your interfaces (which usually start as something like “eth0”, “em1”, or “p1p1” depending on hardware and CentOS version) to something a little more useful. Here’s how.







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VMWare Tools Upgrades for CentOS Systems

by on Jun.27, 2012, under Computers, Technology

Just a quickie post outlining something I ran into; I installed/upgraded VMWare Tools and ended up having no Ethernet device. This is what I think would be a streamlined procedure to get things where they should be.







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Creating your own CentOS 6.2 LiveDVD

by on Jun.12, 2012, under Computers, Technology

When I started, I had no real knowledge of kickstart files. Now I know a little, and I figured I could share with other CentOS/Red Hat admins how one might customize a kickstart file to create a LiveDVD ISO.







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Increasing a CentOS Linux LVM partition size, the dangerous way

by on Feb.23, 2012, under Computers, Technology

There are two ways to do this – the easy, safe way, and the somewhat cleaner but more dangerous way. I’ll be providing the steps for doing it the not quite so easy, somewhat more dangerous way, as it makes your partitions look nicer. This is probably the most unsafe way to do it, and there’s probably easier ways to accomplish what I’m trying to do, but here’s what appears to have worked.







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CentOS, cisco monitor ports, and IPv6

by on Jan.15, 2012, under Networking, Technology

I finally got the job I’ve been wanting for, oh, nearly a decade now (if not more). In this job I’m the go-to admin for the servers (almost all CentOS based) that support a large (3000+ device) network. Cisco routers run the network, and we have servers that are connected to “monitor” ports. One of the principle tasks of these servers are to allow network engineers to run packet captures. Thing is, interesting things can happen as far as IPv6 is concerned when you have systems getting IPv6 router advertisements on server interfaces that don’t actually do more than just accept packets …







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