<html><head><style>body{font-family:Helvetica,Arial;font-size:13px}</style></head><body><div style="font-family:Helvetica,Arial;font-size:13px">Khalid ,</div><div style="font-family:Helvetica,Arial;font-size:13px"> Happy New Year! I recommend not using the default tty paths, they are not deterministic and can get modified by different hardware detection ordering. That can be caused by unplugging and replugging, driver reloading, and/or kernel changes that change the order devices are listed in.</div><div style="font-family:Helvetica,Arial;font-size:13px"><br></div><div style="font-family:Helvetica,Arial;font-size:13px">Use the paths under </div><div style="font-family:Helvetica,Arial;font-size:13px"> /dev/serial/by-id/</div><div style="font-family:Helvetica,Arial;font-size:13px"><br></div><div style="font-family:Helvetica,Arial;font-size:13px">These paths include unique identifiers which ensure when the same device is detected it will be provided under a reliable name/path.</div><div style="font-family:Helvetica,Arial;font-size:13px"><br></div><div style="font-family:Helvetica,Arial;font-size:13px">Think of this like the changes in fstab where there was a change from using device paths to using volume ids(a.k.a. UUIDs) to ensure when drives were detected out of order they still functioned without issue. </div><div style="font-family:Helvetica,Arial;font-size:13px"><br></div><div style="font-family:Helvetica,Arial;font-size:13px">In a side note, once I nearly caused a major outage due to using a UUID rather than a path.</div><div style="font-family:Helvetica,Arial;font-size:13px"><br></div><div style="font-family:Helvetica,Arial;font-size:13px">I took a snapshot of a XFS volume before doing some maintenance. When I rebooted everything came back up but when I tried to delete the snapshot it was still in use. </div><div style="font-family:Helvetica,Arial;font-size:13px"><br></div><div style="font-family:Helvetica,Arial;font-size:13px">I couldn’t figure out what was going on until I closed my eyes in bed about 8 hours later when suddenly I realized the snapshot had the same UUID as the base volume and the system had in fact booted from it rather than the base volume. I called the office and told them to wake the IT chain to director level as we would have a high severity outage when the snapshot ran out fo space in 4 hours. </div><div style="font-family:Helvetica,Arial;font-size:13px"><br></div><div style="font-family:Helvetica,Arial;font-size:13px">In the end, we stopped our data processing pipeline, wait for all the in process work to complete, and then rebooted back into the original boot/base volume. We lost about 8 hours of records but managed to limit downtime to about 10 minutes and didn’t miss any transactions of importance. We backed up the snapshot just in case any of the missing data was needed but it never was even noticed.</div> <br> <div class="gmail_signature"></div> —Tim<div><br><p class="airmail_on">On January 2, 2022 at 9:37:35 PM, Khalid Baheyeldin (<a href="mailto:kb@2bits.com">kb@2bits.com</a>) wrote:</p> <blockquote type="cite" class="clean_bq"><span><div><div></div><div><div dir="ltr"><div>So here is the situation. <br></div><div>I have a few serial devices and they behave well.</div><div>Each gets the device /dev/ttyUSB0 device when plugged. <br></div><div>They use the cp210x driver. <br></div><div><br></div><div>No issues for years. <br></div><div><br></div><div>Until today. <br></div><div>Somehow a wrong a sequence, maybe unplugging while a program is still accessing the device, <br></div><div>made every device that gets plugged in get /dev/ttyUSB1 instead of 0.</div><div><br></div><div>No matter what I do, it stays 1. I tried the following:</div><div><br></div><div>sudo udevadm control --reload</div><div>sudo service udev restart</div><div>sudo rmmod cp210x <br></div><div>rmmod: ERROR: Module cp210x is in use</div><div>But nothing is plugged in.</div><div><br></div><div>Trying to force it does not work either:</div><div><br></div><div>sudo rmmod -f cp210x<br>rmmod: ERROR: ../libkmod/libkmod-module.c:799 kmod_module_remove_module() could not remove 'cp210x': Resource temporarily unavailable<br>rmmod: ERROR: could not remove module cp210x: Resource temporarily unavailable</div><div><br></div><div>I know a reboot will fix it, but I don't want to keep rebooting if this happens again. <br></div><div><br></div><div>Any other ideas?</div><br><div><div>-- <br><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature">Khalid M. Baheyeldin<br><a href="http://2bits.com" target="_blank">2bits.com</a>, Inc.<br>Fast Reliable Drupal<br>Drupal performance optimization, hosting and consulting.<br>"Sooner or later, this combustible mixture of ignorance and power is going to blow up in our faces." -- Dr. Carl Sagan</div></div></div></div>
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