:How do I fix known bugs in Linux system software?

A port conflict occurs when you start a service or a process on a CentOS or RHEL 7 instance

Problem description

When you start a service or a process on an ECS instance that runs a specific version of CentOS or RHEL 7, an error message appears indicating a port conflict, and the process cannot be started or the service becomes unavailable. You run the netstat command to query port usage and find that the port used by the service or process is already being used by dhclient, as shown in the following figure. dhclient is short for Internet Systems Consortium (ISC) Dynamic Host Configuration Protocol (DHCP) client.

Cause

In normal cases, dhclient listens for DHCP version 4 (DHCPv4) packets on port 67 or 68 and DHCP version 6 (DHCPv6) packets on port 546 or 547. ECS instances that run specific versions of CentOS or RHEL 7 come with a dhclient version earlier than 4.2.5-60. The versions of dhclient that are earlier than 4.2.5-60 contain bugs and may listen on ports other than ports 67, 68, 546, and 547. If other services or processes on the ECS instances also use the preceding ports, port conflicts may occur and the other services or processes may fail to be started or may become unavailable.

Solution

Upgrade the dhclient package on the CentOS or RHEL 7 instance to the latest version. For more information, see the Upgrade specific software packages to the latest versions or Upgrade all software packages to the latest versions section of this topic.

Slow SSH connection to a CentOS or RHEL 7 instance that is running for an extended period of time

Problem description

If a CentOS or RHEL 7 instance is running for an extended period of time, an SSH connection to the instance may become slow. You run a command to query the CPU utilization of system processes and find that the systemd-logind process runs at 100% CPU utilization. Messages that are similar to the following messages appear in the system logs of the CentOS or RHEL 7 instance:

# journalctl -u dbus
Mar 30 17:23:19 localhost dbus[21]: [system] Activating via systemd: service name='org.freedesktop.login1' unit='dbus-org.freedesk...
Mar 30 17:23:42 localhost dbus[21]: [system] Failed to activate service 'org.freedesktop.login1': timed out...

Cause

The preceding issue occurs due to known bugs in the systemd-logind and D-Bus components. You can resolve the issue by upgrading the preceding components.

Solution

Upgrade the dbus package to the latest version on the CentOS or RHEL 7 instance. For more information, see the Upgrade specific software packages to the latest versions or Upgrade all software packages to the latest versions section of this topic.

Upgrade specific software packages to the latest versions

1. Connect to the Linux ECS instance. For more information, see Connection method overview.

2. Upgrade a specific software package to the latest version.

   The commands that you can use to upgrade a software package vary based on the operating system.

   • Command that you can use on Alibaba Cloud Linux 2.1903, AnolisOS 7, CentOS 7 or earlier, and RHEL 7 or earlier:

     sudo yum update <Software package name>

     For example, to upgrade the dhclient package to the latest version, run the following command:

     sudo yum update dhclient

   • Command that you can use on AlmaLinux, AnolisOS 8 or later, CentOS 8 or later, CentOS Stream 8 or later, Fedora 33 or later, RHEL 8 or later, and Rocky Linux:

     sudo dnf update <Software package name>

     For example, to upgrade the dhclient package to the latest version, run the following command:

     sudo dnf update dhclient

   • Commands that you can use on Debian and Ubuntu:

     # Update the software repository information that is stored on your on-premises device to obtain the latest information about software packages.
     sudo apt update
     # Upgrade a specific software package to the latest version.
     sudo apt upgrade <Software package name>

     For example, to upgrade the dhclient package to the latest version, run the following commands:

     sudo apt update
     sudo apt upgrade dhclient

   • Commands that you can use on openSUSE and SUSE Linux Enterprise Server:

     # Update the software repository information that is stored on your on-premises device to obtain the latest information about software packages.
     sudo zypper refresh
     # Upgrade a specific software package to the latest version.
     sudo zypper update <Software package name>

     For example, to upgrade the dhclient package to the latest version, run the following commands:

     sudo zypper refresh
     sudo zypper update dhclient

The following command output indicates that the dhclient package is upgraded.

Upgrade all software packages to the latest versions

1. Connect to the Linux ECS instance. For more information, see Connection method overview.

2. Upgrade all software packages to the latest versions. The commands that you can use to upgrade all software packages vary based on the operating system.

   • Command that you can use on Alibaba Cloud Linux 2.1903, AnolisOS 7, CentOS 7 or earlier, and RHEL 7 or earlier:

     sudo yum update

   • Command that you can use on AlmaLinux, AnolisOS 8 or later, CentOS 8 or later, CentOS Stream 8 or later, Fedora 33 or later, RHEL 8 or later, and Rocky Linux:

     sudo dnf update

   • Commands that you can use on Debian and Ubuntu:

     # Update the software repository information that is stored on your on-premises device to obtain the latest information about software packages.
     sudo apt update
     # Upgrade all installed software packages to the latest versions.
     sudo apt upgrade

   • Commands that you can use on openSUSE and SUSE Linux Enterprise Server:

     # Update the software repository information that is stored on your on-premises device to obtain the latest information about software packages.
     sudo zypper refresh
     # Upgrade all installed software packages to the latest versions.
     sudo zypper update