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Chapter 21. Shells and command-line tools
The following chapters contain the most notable changes to shells and command-line tools between RHEL 8 and RHEL 9.
21.1. Notable changes to system management
Data Encryption Standard (DES) algorithm is not available for net-snmp communication in Red Hat Enterprise Linux 9
In previous versions of RHEL, DES was used as an encryption algorithm for secure communication between net-snmp clients and servers. In RHEL 9, the DES algorithm isn’t supported by the OpenSSL library. The algorithm is marked as insecure and the DES support for net-snmp has therefore been removed.
The ABRT tool has been removed
The Automatic Bug Reporting Tool (ABRT) for detecting and reporting application crashes is not available in RHEL 9.
As a replacement, use the systemd-coredump tool to log and store core dumps, which are automatically generated files after a program crashes.
The hidepid=n mount option is not supported in RHEL 9 systemd
The mount option hidepid=n, which controls who can access information in /proc/[pid] directories, is not compatible with systemd infrastructure provided in RHEL 9.
In addition, using this option might cause certain services started by systemd to produce SELinux AVC denial messages and prevent other operations from being completed.
The dump utility from the dump package has been removed
The dump utility used for backup of file systems has been deprecated in Red Hat Enterprise Linux 8 and is not available in RHEL 9.
In RHEL 9, Red Hat recommends using the tar, or dd as a backup tool for ext2, ext3, and ext4 file systems. The dump utility will be a part of the EPEL 9 repository.
Note that the restore utility from the dump package remains available and supported in RHEL 9 and is available as the restore package.
RHEL 9 does not contain ReaR crontab
The /etc/cron.d/rear crontab in the rear package, which runs rear mkrescue after the disk layout changes, has been removed in RHEL 9.
If you relied on the /etc/cron.d/rear crontab to run rear mkrescue, you can manually configure periodic runs of ReaR instead.
The rear package in RHEL contains the following examples for scheduling jobs:
-
the
/usr/share/doc/rear/rear.cronexample crontab -
the
/usr/share/doc/rear/rear.{service,timer}example systemd unit
Do not use these examples without site-specific modifications or other actions to take updated backups for system recovery. You must take regular backups in addition to re-creating the rescue image. The steps to take a backup depend on the local configuration. If you run the rear mkrescue command without taking an updated backup at the same time, the system recovery process would use a previous backup that might be inconsistent with the saved layout.
21.2. Notable changes to command-line tools
Support for the raw command-line tool has been removed
With this release, the raw (/usr/bin/raw) command-line tool has been removed from the util-linux package, because Linux kernel does not support raw devices since version 5.14.
Currently, there is no replacement available.
cgroupsv1 is deprecated in RHEL 9
cgroups is a kernel subsystem used for process tracking, system resource allocation and partitioning. Systemd service manager supports booting in the cgroups v1 mode and in cgroups v2 mode. In Red Hat Enterprise Linux 9, the default mode is v2. In the next major release, systemd will not support booting in the cgroups v1 mode and only cgroups v2 mode will be available.
The lsb-release binary is not available in RHEL 9
The information in the /etc/os-release file was previously available by calling the lsb-release binary. This binary was included in the redhat-lsb package, which was removed in RHEL 9. Now, you can display information about the operating system, such as the distribution, version, code name, and associated metadata, by reading the /etc/os-release file. This file is provided by Red Hat and any changes to it are overwritten with each update of the redhat-release package. The format of the file is KEY=VALUE, and you can safely source the data for a shell script.
