CentOS/RHEL 7

This post explains how to change the ulimit limits such as the maximum open files for a systemd service. In a CentOS/RHEL 7 or 8 system, the changes done in /etc/security/limits.conf or /etc/security/limits.d/ have no effect on systemd services. Systemd deliberately ignores the system-wide ulimit settings in order to minimize unintentional or unexpected limit changes […]

The Problem Starting ssh services errors out and spool messages regarding polkit service. # service sshd restart Redirecting to /bin/systemctl restart sshd.service Authorization not available. Check if polkit service is running or see debug message for more information. Same issue is encountered when starting the polkit service. # service polkit restart Redirecting to /bin/systemctl restart […]

Network interface teaming was introduced from CentOS/RHEL 7 as a more extensible and scalable alternative to network bonding. This post describes how to configure network teaming on CentOS/RHEL 7/8. The examples provided are based on Oracle Linux 8.2 system (Oracle VirtualBox 6.1 guest virtual machine) with two network interfaces using NetworkManager. Specifically, the Network Manager […]

This post explains how to find the OS version which was first installed on a CentOS/RHEL system. CentOS/RHEL 6 Run grep -m1 “label =” /var/log/anaconda.storage.log to find the original installation OS version. Current version: # cat /etc/redhat-release CentOS Linux release 6.10 Original installation version: # grep -m1 “label =” /var/log/anaconda.storage.log label = EL6.8_x86_64_Disc_1_20160518 size = […]

Question: How to Calculate the percentage of memory reserved by Huge Pages? 1. Inspect the memory parameters: # cat /proc/meminfo MemTotal: 98721456 kB MemFree: 1277612 kB MemAvailable: 12186676 kB Buffers: 20496 kB Cached: 11013124 kB SwapCached: 4820 kB Active: 2303780 kB Inactive: 9716992 kB Active(anon): 716672 kB Inactive(anon): 582092 kB Active(file): 1587108 kB Inactive(file): 9134900 […]

The Problem Unable to start polkitd service, which in turn affects other services as well. # systemctl restart polkit ** (pkttyagent:32189): WARNING **: 13:59:48.884: Unable to register authentication agent: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.PolicyKit1 was not provided by any .service files Error registering authentication agent: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name org.freedesktop.PolicyKit1 was not provided by any .service files […]

This note exemplifies how to configure VLAN on bonding network interface on CentOS/RHEL 7 and 8. The configuration of the switch to support VLAN tagging is not covered in this note. You do not need to do anything for configuring native VLAN on CentOS/RHEL, since it only depends on the switch configuration. 1. Check that […]

Problem /tmp is not automatically mounted after reboot even though an entry is present in /etc/fstab. Below outputs show an example of the issue: # uptime 16:44:11 up 2 min, 1 user, load average: 0.21, 0.55, 0.44 # df -h Filesystem Size Used Avail Use% Mounted on devtmpfs 252G 0 252G 0% /dev tmpfs 252G […]

This post will show how to Disable the HMAC MD5 and the CBC ciphers as an example for CentOS/RHEL 6 and 7. For CentOS/RHEL 7 For more information please look at the man pages: # man sshd_config Ciphers Specifies the ciphers allowed. Multiple ciphers must be comma-separated. If the specified value begins with a ‘+’ […]

This post will help to disable TLS 1.1 cockpit port 9090. 1. Create file /etc/systemd/system/cockpit.service.d/ssl.conf containing: [Service] Environment=G_TLS_GNUTLS_PRIORITY=NORMAL:-VERS-SSL3.0:-VERS-TLS1.0:-VERS-TLS1.1 2. Reload systemd daemons: # systemctl daemon-reload 3. Restart cockpit service: # systemctl restart cockpit 4. Check protocols tls1_1: # echo test | openssl s_client -connect localhost:9090 -tls1_1CONNECTED(00000003) 139687924594576:error:1408F10B:SSL routines:SSL3_GET_RECORD:wrong version number:s3_pkt.c:365: — no peer certificate available […]