Ever wonder why repetitive pings fail after a little while in OS X (e.g. those sent via the -f flag)? By default, OS X has an ICMP rate limit of 250 set. You can increase this or disable, using sysctl. To disable, set the value of net.inet.icmp.icmplim sudo sysctl -w net.inet.icmp.icmplim=0 Happy icmp flooding!
-
-
Managing Core Dumps
The core dump is a memory image of a processes in-core state that is written to the /cores directory by default and is named core followed by a . and then the pid number. So if a process with pid 87 crashes a file is written by default at /cores/core.87. The feature can be turned off using sysctl, along with the kern.coredump MIB, setting it to 0 (by default it’s 1). sysctl kern.coredump=0 To turn it back on: sysctl kern.coredump=1 Additionally, you can change the path that the files are written into, using sysctl along with the kern.corefile MIB. The corefile is an expression that by defualt writes core.%P where…
-
Using sysdiagnose to Capture Performance Data In OS X
“My computer sometimes just runs slow,” “the fan on my laptop won’t turn off sometimes,” and “my network connection keeps dropping.” These are amongst the most annoying off problems to solve for our users because they are intermittent. And to exacerbate things, many of these users have these problems at home or at remote locations, making it difficult for systems administrators to see them. There is something I use in these cases, though, that has helped isolate these problems from time to time. Simply tell users to Control-Option-Command-Shift-Period when they have these problems. Doing so will run the sysdiagnose command and then open a Finder window with the output of the…
-
Installing Ubuntu 10 in Fusion
I’ve done a number of articles on using Ubuntu 10 as a server recently, but haven’t actually looked at doing the base installation of an Ubuntu 10 host. In this example, I’ll look at using Ubuntu 10.04 Desktop. In many of the previous examples I’ve been looking at Ubuntu 10.10 Server; the reason I’m using 10.04 Desktop here is because I believe there is a smaller learning curve and that inherently Mac OS X Systems Administrators who might be following this thread actually like a GUI. There are a number of aspects of this type of setup that are simply not GUI oriented; however, the base OS can easily be,…
-
Bakbone: SysCtl and Shared Memory Hax0r to get Bakbone to Play Nice
Shared Memory Tweaking: 1GB Shared memory (set in /etc/sysctl.conf) kern.sysv.shmall: 262144 kern.sysv.shmseg: 32 kern.sysv.shmmni: 128 kern.sysv.shmmin: 1 kern.sysv.shmmax: 1073741824
-
vnode
The vnode table represents all file activity in UNIX. There is a unique vnode allocated in the vnode table for each active file, each current directory, each mounted-on file, text file, and the root. To see the number of vnodes available in Mac OS X, look to sysctl for the kern.maxvnodes variable using something similar to the following command: sysctl -A | grep vnode