To perform the lookup, you fire NAME::lookup, to retrieve the data, you call NAME::resolved. But the lookup command, and the response command (NAME::response). Thus, there are really two commands to deal with when looking at NAME::lookup. At the time it was implemented this was required as there was no way to have the command suspend the connection as necessary, execute the query and return with the value retrieved in an efficient, reliable manner. You might think that's a bit awkward, that the command being executed to do a lookup doesn't actually return the value of the lookup. This command does not directly return a value The major issues to note here that have historically made this a bit cumbersome are:ġ. The command is simple, and takes either an IP or Hostname as an argument, performing the appropriate lookup on that string as necessary. It still works, and many people, myself included, have used it to great success in the past. This command was introduced in v9, so it's been around for years now. I'm simply documenting both and comparing them to clear up questions and issues that might be faced by those migrating or that don't understand the differences and pros/cons. We'll take a look at both, but I'll clearly say it up front, RESOLV::lookup is the preferred method of resolution these days. There are two ways of performing DNS queries via a native iRule command: NAME::lookup, and RESOLV::lookup. Sure, that was a while ago, but I still run into this from time to time where people don't know the differences between the old and new methods, so I figured it was high time to put them down here. What was a nice surprise, however, was when the name resolution game got changed as of BIG-IP v10.1. Whether it's querying an address before routing traffic, securing access of an application to only particular segments, or simply using DNS as a high-speed DB to store whatever other information you want, the possibilities are broad and deep.įor those of you that have been familiar with DNS queries via iRules for a while now, that should come as no surprise. Perhaps not as widely used as the HTTP or string commands, but the times that it does get used it solves problems that simply couldn't be solved any other way, often times. 2>&1 means to input the error information into log.txt, 2 Refers to the standard input and output error (stderr), 1 refers to the standard output (stdout), 2> & 1 means 2 is equivalent to 1 output, the last & is the meaning of background operation, combined with the nohup command.There are so many things that you can do with iRules that it can be pretty staggering to narrow down what the "most useful" commands are, but if I were given that task and absolutely had to, I would say that DNS resolution ranks up there pretty high on the most powerful list. “>log.txt” refers to redirecting the output to log.txt. ![]() Nohup matlab -nodesktop -nosplash -nodisplay log.txt 2>&1 & In this case, using the following command instead: The above command may output Bad file descriptor and Warning: “Error reading Character from command line” error. Command: nohup matlab -r MatlabScriptName -nodisplay - nosplash -nojvm -nodesktop &.Step 2: Run Matlab without GUI and in the background Command: module load apps/MATLAB/R2020a. ![]() Unload a module: module unload apps/MATLAB/R2020a. ![]()
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