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(2017-09-13) Changing Grub Parameters With Grubby for KERNEL in /boot/vmlinuz-*; do grubby --update-kernel="$KERNEL" --remove-args="rhgb quiet" grubby --update-kernel="$KERNEL" --args="elevator=noop" done

(2016-11-21) Problem Setting the computer's hostname hasn't changed for the last 20 years or so. This is a boring state of affairs, we need some different, unintuitive way of setting it, ideally hopelessly integrated into systemd somehow. Solution # hostnamect...

(2018-08-21) Problem RHEL 7 doesn't have "grub" command for making RAID-1 disks bootable. Alleged Solution ...assuming /boot on /dev/mdXXX is on sdaX and sdbX # grub2-install /dev/sda # grub2-install /dev/sdb "Alleged" for now because I have not had the occas...

(2019-09-11) Examples # journalctl -u vmtoolsd --since=today # journalctl -u sshd # journalctl --since=yesterday --until=now # journalctl --since "2023-12-01 10:00:00" --until "2023-12-01 12:00:00" # journalctl -f # journalctl --disk-usage

(2017-04-28) Problem Can't use passwordless ssh to a target system. Solution In this particular case, I have: a home directory on nfs selinux enabled In this combination, the sshd process can't read the private key in the user's home directory. There are a c...

(2021-02-23) Installing PHP 7 Instructions for7.4 Older information (2017-09-13) CentOS 7 provides PHP version 5.4 in its official repository. Command to install the Remi repository configuration package: yum install http://rpms.remirepo.net/enterprise/remi-re...

(2019-03-15) Problem Unable to negotiate with $IP port 22: no matching cipher found. Their offer: aes128-cbc,3des-cbc,aes192-cbc,aes256-cbc Solution $ ssh -c aes128-cbc user@$IP Commentary I don't know where your ship learned to communicate, sir, but it has t...

(5 September 2019) Problem When I ssh login to a CentOS 7 system, it always takes around 30 second to log in. Solution Turn off the authentication types you don't need in /etc/ssh/sshd_config : useDNS no ChallengeResponseAuthentication no KerberosAuthenticatio...

(2014-01-20) Problem Email: ################# SSL Certificate Warning ################ Certificate for hostname 'computer.domain', in file (or by nickname): /etc/pki/tls/certs/localhost.crt The certificate needs to be renewed; this can be done usi...

(2018-06-19) Problem I want a network interface on my CentOS 7 system to start at boot time but I don't want it to have an IP address. Solution Define the interface with a static IP, then edit /etc/sysconfig/network-scripts/ifcfg-$INTERFACE and comment out the...

God Damnit What How List services systemctl list-unit-files Start service at boot time systemctl enable $service Start service now systemctl start $service

(2017-05-04) Problem Test Sendmail's TLS configuration. Solution $ openssl s_client -starttls smtp -connect localhost:25 This should return a gratuitous barf telling you all about the TLS configuration.

(2018-01-12) Problem I need a tftp server on CentOS 7. Solution # yum -y install tftp-server xinetd # systemctl start tftp-server # vi /etc/xinetd.d/tftp (edit disabled = no) # systemctl start xinetd # firewall-cmd --add-service=tftp If you need this config ...

(2019-09-13) Problem VM transplanted between two VMware clusters. Ran fine in old cluster for two years. In the new cluster, the VM goes unavailable for seemingly random periods of time. In the VM, syslog is logging: Sep 9 13:46:10 n2 NetworkManager[695]: <in...

Problem vsftpd in user chroot mode. When logging in, you get: 500 OOPS: chroot Solution You have selinux enabled. In RedHat Enterprise 7.3, the selinux boolean ftp_home_dir was removed. So your choices are either: disable selinux; or grant ftpd full access t...

(2020-05-03) Docker on CentOS 8 # dnf config-manager --add-repo=https://download.docker.com/linux/centos/docker-ce.repo # dnf install https://download.docker.com/linux/centos/7/x86_64/stable/Packages/containerd.io-1.2.6-3.3.el7.x86_64.rpm # dnf install docker-...

(2021-08-17) Problem: Some variety of libGL error: MESA-LOADER: failed to open swrast: /usr/lib64/dri/swrast_dri.so: cannot open shared object file: No such file or directory (search paths /usr/lib64/dri) libGL error: failed to load driver: swrast In my case ...

(2021-02-17) Problem A system between me and my destination is doing proxying for the destination IP. In practice: A firewall was showing all IPs it could route to as having SIP and Cisco-CSSP services enabled. Configuration changes to the firewall were necess...