Author: leizhou


About this author:

6020095 · 2^6972593 – 1 is prime

It has 2098967 decimal digits. See record page here.

3^1681130 + 3^445781 + 1 is prime.

Proof file: HERE Record page here. 3^1681130+3^445781+1 has 802,104 digits factor of p-1: 3^1681130+3^445781 = 3^445781*(3^1235349+1) for 3^1235349+1: Divisor of 1235349: {1, 3, 9, 317, 433, 951, 1299, 2853, 3897, 137261, 411783, 1235349} for which Cyclotomic[2x,3] divides 3^1235349+1, 3^1235349+1=Product of Phi[2m,3], m is in the above divisor list. Phi: Cyclotomic function in Mathematica. Phi[2,3] = […]

NFS_v4 stall, how to rescure without reboot

Sometimes your NFS mount stopped response. You cannot umount normally, if you use umount -l to unmount it, you cannot mount it again, Mounting attempt stalls too. The suggestion on the interenet was to just reboot the client. But you may have important jobs or services on it and you really do not want to. […]

dnf install/update fail with error rpmdbNextIterator skipping Header V3 RSA/SHA1 Signature BAD

Sometimes when an dnf update was unexpectedly terminated like a power failure, the system may leave an inconsistent rpm database. If this happens, in most case by rebuilding rpm database (rpmdb –rebuilddb), and to use (package-cleanup –cleandupes), it could be fixed. For some severe case, after both, when you are trying to run (dnf update […]

ssh command does not exit when X11 forwarding is enabled

If ForwadX11 and ForwardX11Trusted are both enabled in /etc/ssh/ssh_config, when you do “ssh host” it will invoke X11 forwarding by default. This is convenient when you frequently need to run programs with GUI on remote host. However, with X11 forwarding, if you are simply running a text mode command/script via ssh, like “ssh node ls” […]

ssh pass password to sudo

echo <your password> | ssh <node name> “sudo -S <command>”

Recovering LVM from disk image

For a RAID NAS box, when the NAS box dies, the data on the drives are still intact. They can be retrieved in the following steps: dd disks containing LVM to hard drive; # create images of hard drives losetup /dev/loopx disks.img; # make images appear as loop devices on OS partx -v -add /dev/loopx; […]

bash script does not run command

Sometimes a bash script does not run the commands as cron or start up scripts that usually run when you debugging it. This may be caused by that the embedded running environment does not provide proper search path. To avoid this, always use full path to the executibles.

R upgrade all packages

update.packages(checkBuilt=TRUE, ask=FALSE)

Fedora copy paste not working

The convenient select copy, mouse middle click paste way does not work on some Fedora desktop environment. Even the Ctrl-C/Ctrl-V/Ctrl-X copy past and menu copy-paste does not work, forcing users to hand type in things that usually just a few mouse clicks away. This is identified as a buggy package called “clipit” To identify the […]