Common Skills

• Common Skills
  • Configuring the Network
  • Managing RPM Packages
  • Configuring SSH

Configuring the Network

1. Configure the IP address.

   Run the ip command to configure an address for the interface. interface-name indicates the name of the NIC.

   ip addr [ add | del ] address dev interface-name
   

2. Configure a static IP address.

   # Configure the static IP address.
   ip address add 192.168.0.10/24 dev enp3s0
   
   # Run the following command as the root user to query the configuration result:
   ip addr show dev enp3s0
   
   # The result is as follows:
   2: enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
   link/ether 52:54:00:aa:ad:4a brd ff:ff:ff:ff:ff:ff
   inet 192.168.202.248/16 brd 192.168.255.255 scope global dynamic noprefixroute enp3s0
   valid_lft 9547sec preferred_lft 9547sec
   inet 192.168.0.10/24 scope global enp3s0
   valid_lft forever preferred_lft forever
   inet6 fe80::32e8:cc22:9db2:f4d4/64 scope link noprefixroute
   valid_lft forever preferred_lft forever
   

3. Configure a static route.

   Run the ip route add command to add a static route to the routing table and run the ip route del command to delete a static route. The common format of the ip route command is as follows:

   ip route [ add | del | change | append | replace ] destination-address
   

   • To add a static route to the host address, run the following command as the root user:

   ip route add 192.168.2.1 via 10.0.0.1 [dev interface-name]
   

   • To add a static route to the network, run the following command as the root user:

   ip route add 192.168.2.0/24 via 10.0.0.1 [dev interface-name]
   

4. Configure the network using the ifcfg file.

   Modify the ifcfg-enp4s0 file generated in the /etc/sysconfig/network-scripts/ directory as the root user. The following is an example:

   TYPE=Ethernet
   PROXY_METHOD=none
   BROWSER_ONLY=no
   BOOTPROTO=none
   IPADDR=192.168.0.10
   PREFIX=24
   DEFROUTE=yes
   IPV4_FAILURE_FATAL=no
   IPV6INIT=yes
   IPV6_AUTOCONF=yes
   IPV6_DEFROUTE=yes
   IPV6_FAILURE_FATAL=no
   IPV6_ADDR_GEN_MODE=stable-privacy
   NAME=enp4s0static
   UUID=xx
   DEVICE=enp4s0
   ONBOOT=yes
   

Managing RPM Packages

The full name of RPM is RPM Package Manager, which is intended to manage Red Hat software packages. It is used in mainstream distributions such as openEuler, Fedora, Red Hat, Mandriva, SUSE and YellowDog, and distributions developed based on these distributions.

RPM installs the required software to a set of management programs on the Linux host in database record mode. The software to be installed is compiled and packaged, and the default database record in the packaged software records the dependencies required for the software installation. When a user installs the software on a Linux host, RPM checks whether the dependencies on the Linux host meets the requirements based on the data recorded in it.

• If yes, install the software.
• If no, do not install the software.

During the installation, all software information is written into the RPM database for subsequent query, verification, and uninstallation.

1. Default installation path of the RPM packages

   Generally, RPM uses the default installation path. (The default installation path can be queried by running a command and will be described in detail in subsequent sections.) All installation files are distributed to the directories listed in the following table by type.

   RPM installation paths and their meanings

   Installation Path	Description
   /etc/	Configuration file installation directory
   /usr/bin/	Installation directory of the executable commands
   /usr/lib/	Path for storing the function library used by the program
   /usr/share/doc	Location where the basic software user manual is saved
   /usr/share/man/	Path for saving the help file

   Note: You can manually specify the installation path of RPM, but this method is not recommended. After the installation path is manually specified, all installation files are installed in the specified path, and the command for querying the installation path in the system cannot be used. The command can be identified by the system only after being manually configured.

2. rpm command options

   Checking the RPM Signature of the Software Package

   Before installing the RPM package on a Linux host, check the PGP signature. After ensuring that the signature integrity and source are correct, run the rpm --checksig command to verify the validity:

   rpm --checksig nano-2.3.1-10.el7.x86_64.rpm
   

   Installing RPM Packages

   To install RPM packages in Linux, use the -i option in the rpm command.

   rpm -ivh nano-2.3.1-10.el7.x86_64.rpm
   

   • -i: installs the software package.
   • -v: displays detailed information.
   • -h: lists flags during suite installation.

   Querying an Installed RPM Package

   To query an RPM package (dnf) installed in the Linux system, use the -q option in the rpm command.

   rpm -q dnf
   

   • -q: query operation

   If the specified package is not installed, the following error message is displayed:

   package dnf is not installed
   

   Querying All Installed RPM Packages

   To query all RPM packages installed in Linux, use the -qa option in the rpm command.

   $ rpm -qa 
   dracut-config-rescue-055-7.oe2203sp2.x86_64
   parted-3.5-1.oe2203sp2.x86_64
   irqbalance-1.8.0-9.oe2203sp2.x86_64
   ......
   

   Note: When using the -qa option, use the pipe character (|) together to improve the search accuracy.

   Querying Details About an Installed RPM Package

   Use the -qi option in the rpm command to query the details of an RPM package installed in the system.

   # rpm -qi python3
   Name        : python3
   Version     : 3.9.9
   Release     : 24.oe2203sp2
   Architecture: x86_64
   Install Date: Wed 30 Mar 2022 08:30:23 AM UTC
   Group       : Unspecified
   Size        : 35916839
   License     : Python
   Signature   : RSA/SHA1, Wed 30 Mar 2022 03:29:30 AM UTC, Key ID d557065eb25e7f66
   Source RPM  : python3-3.9.9-24.oe2203sp2.x86_64.rpm
   Build Date  : Tue 15 Mar 2022 12:00:00 AM UTC
   Build Host  : obs-worker1639015616-x86-0001
   Packager    : http://openeuler.org
   Vendor      : http://openeuler.org
   URL         : https://www.python.org/
   Summary     : Interpreter of the Python3 programming language
   Description :
   Python combines remarkable power with very clear syntax. It has modules,
   classes, exceptions, very high level dynamic data types, and dynamic
   typing. There are interfaces to many system calls and libraries, as well
   as to various windowing systems. New built-in modules are easily written
   in C or C++ (or other languages, depending on the chosen implementation).
   Python is also usable as an extension language for applications written
   in other languages that need easy-to-use scripting or automation interfaces.
   
   This package Provides python version 3.
   

   Querying All Files in an RPM Package

   To query the file list of an RPM package that is not installed, use the -qlp option in the rpm command.

   $ rpm -qlp pkgship-2.2.0-10.oe2203sp2.noarch.rpm
   /etc/ima/digest_lists.tlv/0-metadata_list-compact_tlv-pkgship-2.2.0-10.oe2203sp2.noarch
   /etc/ima/digest_lists/0-metadata_list-compact-pkgship-2.2.0-10.oe2203sp2.noarch
   /etc/pkgship/auto_install_pkgship_requires.sh
   /etc/pkgship/conf.yaml
   /etc/pkgship/package.ini
   ......
   

   Querying RPM Package Dependencies

   To query the list of dependency packages compiled by a specified RPM package that is not installed, use the -qRp option in the rpm command.

   $ rpm -qRp pkgship-2.2.0-10.oe2203sp2.noarch.rpm
   /bin/bash
   /bin/sh
   /usr/bin/python3
   config(pkgship) = 2.2.0-10.oe2203sp2
   python3
   python3-Flask-Limiter
   ......
   

   Verifying All Installed RPM Packages

   To verify an installed RPM package, use the -Va option in the rpm command to compare the information about the files installed in the package with the information about the files obtained from the package metadata stored in the RPM database.

   $ rpm -Va
   S.5....T.  c /root/.bashrc
   .......T.  c /etc/yum.repos.d/openEuler.repo
   S.5....T.  c /etc/issue
   S.5....T.  c /etc/issue.net
   S.5....T.  c /etc/csh.login
   S.5....T.  c /etc/profile
   .M....G..  g /var/log/lastlog
   .M.......  c /boot/grub2/grubenv
   ......
   

   Output fields of the rpm -Va command and their meanings

   Field	Description
   S	The file length changes.
   M	The access permission or type of a file changes.
   5	The MD5 checksum changes.
   D	The attributes of a device node change.
   L	The symbolic link of a file changes.
   U	The owner of a file, subdirectory, or device node changes.
   G	The group of a file, subdirectory, or device node changes.
   T	The last modification time of a file changes.

   Querying the RPM Package of a Specific File

   To query an RPM package that provides a specific binary file on Linux, use the -qf option in the rpm command.

   $ rpm -qf /usr/share/doc/pkgship
   pkgship-2.2.0-10.oe2203sp2.noarch.rpm
   

   Querying Files in an Installed RPM Package

   To query the list of installation files of an RPM package, use the -ql option in the rpm command.

   $ rpm -ql dnf
   /etc/bash_completion.d/dnf
   /etc/ima/digest_lists.tlv/0-metadata_list-compact_tlv-dnf-4.14.0-14.oe2203sp2.noarch
   /etc/ima/digest_lists/0-metadata_list-compact-dnf-dnf-4.14.0-14.oe2203sp2.noarch
   /usr/bin/dnf
   /usr/lib/systemd/system/dnf-makecache.service
   /usr/lib/systemd/system/dnf-makecache.timer
   /usr/share/doc/dnf
   /usr/share/doc/dnf/AUTHORS
   /usr/share/doc/dnf/README.rst
   /usr/share/licenses/dnf
   /usr/share/licenses/dnf/COPYING
   /usr/share/licenses/dnf/PACKAGE-LICENSING
   /var/cache/dnf
   

   Querying the Recently Installed RPM Packages

   Linux is a multi-user OS. During the use of Linux, other users may have installed some software packages. To query the recently installed packages in the system, use the -qa --last options in the rpm command.

   $ rpm -qa --last
   ntp-4.2.8p15-11.oe2203sp2.x86_64
   ntpstat-0.6-4.oe2203sp2.noarch
   ntp-help-4.2.8p15-11.oe2203sp2.noarch
   

   Querying Only the Documents of the Installed RPM Packages

   You can obtain the help information of any command from the Linux Man page (path for storing /usr/share/doc/Package_Name-Version_Number/docs* documents). To query the list of documents associated with the installed RPM packages, use the -qdf option in the rpm command and enter the binary file path.

   $ rpm -qdf /usr/bin/grep
   /usr/share/doc/grep/NEWS
   /usr/share/doc/grep/README
   /usr/share/doc/grep/THANKS
   /usr/share/doc/grep/TODO
   /usr/share/info/grep.info.gz
   /usr/share/man/man1/egrep.1.gz
   /usr/share/man/man1/fgrep.1.gz
   /usr/share/man/man1/grep.1.gz
   

   Upgrading an Installed RPM Package

   You can easily upgrade the installed RPM package to the latest version by using the -Uvh option and the rpm command.

   $ rpm -Uvh pkgship-2.2.0-10.oe2203sp2.noarch.rpm
   Preparing...        ################################# [100%]
   

   Note: When the installed RPM package is upgraded, the old RPM package is deleted and the new RPM package is installed.

   Removing an Installed RPM Package

   To remove an RPM package installed on the system, use the -ev or -e option in the rpm command.

   rpm -ev pkgship
   

   Rebuilding the Damaged RPM Database

   When you try to update the system using the yum update command, you may receive an error message indicating that the RPM database is damaged. If you receive this message, use the --rebuilddb option in the rpm command to rebuild the database.

   rm /var/lib/rpm/__db*
   rpm --rebuilddb
   

   Checking Whether Vulnerabilities in Specific Packages Have Been Fixed

   You can use the --changelog option in the rpm command and enter the corresponding CVE ID.

   rpm -q --changelog python-2.6.6 | grep -i "CVE-2019-9636"
   

   Importing the RPM GPG Key

   By default, when a new repository is added to the Linux system, the GPG key is automatically imported. You can also use --import in the rpm command to manually import the RPM GPG key to check the integrity of a package when downloading it from the repository.

   rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-OpenEuler-22.03-LTS-SP2
   

3. DNF commands

   DNF commands

   Command	Description
   repolist	Displays the configured software repository source.
   install	Installs one or more software packages on Linux.
   upgrade	Upgrades one or more software packages on Linux.
   list	Lists a software package or a group of software packages.
   info	Displays detailed information about a package or package group.
   updateinfo	Displays the bulletin information about a package.
   search	Searches for the specified character string in the software package details.
   check-update	Checks for software package update.
   remove	Removes one or more software packages from the system.
   reinstall	Reinstalls a package.
   downgrade	Downgrades a software package.
   autoremove	Removes all unnecessary software packages that are installed due to dependency relationships.
   distro-sync	Synchronizes the installed software package to the latest available version.
   makecache	Creates a metadata cache.
   repository-package	Runs commands on all software packages in a specified repository.
   provides	Searches for the software package that provides the specified content.
   group	Displays or uses group information.
   history	Displays or uses transaction history.
   clean	Deletes cached data.

   Displaying Configured Software Repositories

   By default, the --enabled option is added to display the enabled software repositories.

   $ dnf repolist --enabled
   repo id                                                                   repo name
   EPOL                                                                      EPOL
   OS                                                                        OS
   debuginfo                                                                 debuginfo
   everything                                                                everything
   pkgship_elasticsearch                                                     Elasticsearch repositor
   source                                                                    source
   update                                                                    update
   

   • --all: displays all software repositories.
   • --disabled: displays disabled software repositories.
   • --enabled: displays enabled repositories (default).

   Installing One or More Software Packages

   You can run the install command to install RPM packages.

   dnf install software_package
   

   Conflicting packages or packages that cannot be installed may exist during software package installation. You can add --allowerasing to the command to replace the conflicting packages or --skip-broken to skip the packages that cannot be installed.

   dnf install software_package [software_package ...] --allowerasing --skip-broken
   

   When dnf is used to install a software package, add --installroot to set the root directory for installing the software package.

   dnf install software_package --installroot software_package_root_directory
   

   If you need to temporarily specify a repository source for installation, you can add the --setopt=reposdir= option to specify the loading directory of the repository source.

   dnf install software_package --setopt=reposdir=repo_source_directory
   

   If interactive confirmation is not required during installation, you can add -y or --assumeyes to enable all software packages to be installed to automatically answer Yes.

   dnf install software_package -y
   

   To install an RPM package by specifying a specific repository source, you can specify the --repo or --enablerepo option. To achieve the same effect, you can also use the --disablerepo option to disable the matched repository source. You are advised to use the --repo option to install the RPM package.

   dnf install software_package --repo=repo_source_
   

   Reinstalling a Software Package

   You can run the reinstall command to reinstall a software package in the system.

   dnf reinstall software_package
   

   Upgrading One or More Software Packages

   • You can use the upgrade command to upgrade one or more software packages on Linux.

   dnf upgrade software_package [software_package ...]
   

   • You can also run the update command to upgrade one or more software packages.

   dnf update software_package [software_package ...]
   

   Downgrading a Software Package

   If a compatibility problem occurs because the version of a software package is too late, you can downgrade the software package.

   dnf downgrade software_package
   

   Listing a Package or a Group of Packages

   You can run the list command to list the software packages installed in the system and the software packages in the configured repository.

   dnf list
   

   You can add options to filter the displayed package list.

   • --all: displays all software packages (default).
   • --available: displays only available software packages.
   • --installed: displays only installed software packages.
   • --extras: displays only additional software packages.
   • --updates: displays only the software packages to be upgraded.
   • --upgrades: displays only the software packages to be upgraded.
   • --autoremove: displays only the software packages to be removed.
   • --recent: displays the software packages that have been changed recently.

   Querying Details About a Software Package

   You can run the info command to query details about a software package.

   dnf info software_package
   

   Searching for a Software Package

   If you need to install a software package in the system but you are not sure about the full name of the software package, you can run the search command to search for the matched package.

   dnf search software_package
   

   Uninstalling One or More Software Packages

   You can run the remove command to remove an expired or duplicate software package.

   dnf remove software_package
   

   • --duplicates: removes installed (duplicate) software packages.
   • --oldinstallonly: removes expired installation-only software packages.

   Automatically Removing Software Packages Installed Due to Dependency Relationships

   You can run the autoremove command to remove unnecessary software packages that are installed due to dependency relationships.

   dnf autoremove software_package
   

Configuring SSH

1. Introduction to the SSH service

   Secure Shell (SSH) is a reliable protocol that ensures the security of remote login sessions and other network services. The SSH protocol can effectively prevent information leakage during remote management. SSH encrypts transferred data to prevent domain name server (DNS) spoofing and IP spoofing. OpenSSH was created as an open source alternative to the proprietary SSH protocol.

2. Configuring the SSH Service

   # Open and modify the /etc/ssh/sshd_config file.
   vi /etc/ssh/sshd_config
   
   # Restart the SSH service.
   systemctl restart sshd
   
   # Check the SSH service status.
   systemctl status sshd
   

3. Main options in the SSH service configuration file

   $ Specify the SSH protocol version.
   Protocol 2
   
   # Allowed users
   AllowUsers xxx
   
   # Denied users
   DenyUser root
   
   # Configure session timeout.
   ClientAliveInterval 120
   
   # Disable SSH root login.
   PermitRootLogin no
   
   # Configure or change the SSH port number.
   Port 1234
   
   # Disable SSH password authentication.
   PasswordAuthentication no