转载来源：https://computingforgeeks.com/install-snapd-snap-applications-centos-7/

How to Install Snapd and Snap applications on CentOS 7

(Last Updated On: August 21, 2018)

In this guide, I’ll take you through the steps to install and use snapd service on CentOS 7 server. For those new to snap terminology, snap comes from Snappy which is a package management and software deployment system from Canonical. It was originally designed for the Ubuntu phone operating system.

What is a snap?

A snap :

is a squashFS filesystem containing your app code and a snap.yaml file containing specific metadata. It has a read-only file-system and, once installed, a writable area.
is self-contained. It bundles most of the libraries and runtimes it needs and can be updated and reverted without affecting the rest of the system.
is confined from the OS and other apps through security mechanisms, but can exchange content and functions with other snaps according to fine-grained policies controlled by the user and the OS defaults.

What is Snapd?

Snapd is a REST API daemon service that runs on your Linux system to manage snap packages (“snaps“). It interacts with the snap store and provides the command clientsnap used to interact with it. You must install snapd before you can start managing snaps on any Linux distribution.

Why use Snaps?

Snap packages any app for every Linux desktop, server, cloud or device. Snaps are faster to install, easier to create, safer to run, and they update automatically and transactionally so your app is always fresh and never broken. You can bring your own build infrastructure or use ours.

How to Install and Use Snapd on CentOS 7

Follow steps below to install Snapd on CentOS 7 server.

Step 1: Install the COPR plugin and EPEL

Kick off the installation by adding epel repository and installing copr yum plugin.

sudo yum install epel-release
sudo yum install yum-plugin-copr

Then add the repo:

$ sudo yum copr enable ngompa/snapcore-el7Loaded plugins: copr, fastestmirrorYou are about to enable a Copr repository. Please note that this
repository is not part of the main Fedora distribution, and quality
may vary.The Fedora Project does not exercise any power over the contents of
this repository beyond the rules outlined in the Copr FAQ at
<https://fedorahosted.org/copr/wiki/UserDocs#WhatIcanbuildinCopr>, and
packages are not held to any quality or securty level.Please do not file bug reports about these packages in Fedora
Bugzilla. In case of problems, contact the owner of this repository.Do you want to continue? [y/N]: y
copr done

Once the repository has been added, install snapd package.

sudo yum -y install snapd

Wait for the installation to finish then enable snapd socket:

$ sudo systemctl enable --now snapd.socket
Created symlink from /etc/systemd/system/sockets.target.wants/snapd.socket to /usr/lib/systemd/system/snapd.socket.

Classic confinement requires snaps under /snap or symlink from /snap to /var/lib/snapd/snap. Create a symlink for it like below:

sudo ln -s /var/lib/snapd/snap /snap

Snapd is now ready for use. You interact with it using the snap command. See help page below:

# snap --help
Usage:snap [OPTIONS] <command>Install, configure, refresh and remove snap packages. Snaps are
'universal' packages that work across many different Linux systems,
enabling secure distribution of the latest apps and utilities for
cloud, servers, desktops and the internet of things.This is the CLI for snapd, a background service that takes care of
snaps on the system. Start with 'snap list' to see installed snaps.Application Options:--version  Print the version and exitHelp Options:-h, --help     Show this help messageAvailable commands:abort       Abort a pending changeack         Adds an assertion to the systemalias       Sets up a manual aliasaliases     Lists aliases in the systembuy         Buys a snapchanges     List system changesconnect     Connects a plug to a slotdisable     Disables a snap in the systemdisconnect  Disconnects a plug from a slotdownload    Downloads the given snapenable      Enables a snap in the systemfind        Finds packages to install (aliases: search)get         Prints configuration optionshelp        Helpinfo        show detailed information about a snapinstall     Installs a snap to the systeminterface   Lists snap interfacesinterfaces  Lists interfaces in the systemknown       Shows known assertions of the provided typelist        List installed snapslogin       Authenticates on snapd and the storelogout      Log out of the storelogs        Retrieve logs of servicespack        pack the given target dir as a snapprefer      Prefer aliases from a snap and disable conflictsrefresh     Refreshes a snap in the systemremove      Removes a snap from the systemrestart     Restart servicesrevert      Reverts the given snap to the previous staterun         Run the given snap commandservices    Query the status of servicesset         Changes configuration optionsstart       Start servicesstop        Stop servicesswitch      Switches snap to a different channeltasks       List a change's tasks (aliases: change)try         Tests a snap in the systemunalias     Unalias a manual alias or an entire snapversion     Shows version detailswatch       Watch a change in progresswhoami      Prints the email the user is logged in with.

How to Install Snap Applications on CentOS 7

We use snap command line tool to interact with snaps available on Snap Store.

Searching for a snap:

To search for Snaps, use

$ snap find <search terms>

This will query the store and list the results with their version number, developer names, and the description.

I’ll do an example for installation of Microsoft PowerShell automation and configuration management platform on CentOS 7 server.

# snap search powershell
Name                Version          Developer             Notes    Summary
powershell-preview  6.1.0-preview.4  microsoft-powershell  classic  PowerShell for every system!
powershell          6.0.4            microsoft-powershell  classic  PowerShell for every system!

Install snap by running:

sudo yum install -y icu
sudo snap install powershell --classic

Wait for the download to finish, it should take short time to complete. Since the binary file is located under,/snap/bin/ we need to add this to the $PATHvariable.

$ sudo vim /etc/profile
export PATH="$PATH:/snap/bin/"

Source the file to get new PATH

source /etc/profile

Test by starting the pwshsession.

# pwsh
PowerShell v6.0.4
Copyright (c) Microsoft Corporation. All rights reserved.https://aka.ms/pscore6-docs
Type 'help' to get help.PS /root>

To list installed snaps:

# snap list
Name        Version    Rev   Developer             Notes
core        16-2.34.3  5145  canonical             core
powershell  6.0.4      8     microsoft-powershell  classic

Manually update snaps by running snap refresh

# snap refresh powershell
snap "powershell" has no updates available

Removing Snaps

To remove a snap, all you need to do is run.snap remove <snap name> In our case just do:

# snap remove powershell
powershell removed

Check snap info:

Use the command snap info to check for more info about a snap package.

[root@cent-01 ~]# snap info powershell
name:      powershell
summary:   PowerShell for every system!
publisher: microsoft-powershell
contact:   https://github.com/powershell/powershell
description: |PowerShell is an automation and configuration management platform.It consists of a cross-platform (Windows, Linux, and macOS)command-line shell and associated scripting language.Seehttps://docs.microsoft.com/en-us/powershell/scripting/powershell-core-supportfor support details.
snap-id:     JSNnoJl3EqkMuWoy5Dgq8PMqZ0uNcpie
channels:              stable:    6.0.4 (8) 58MB classiccandidate: 6.0.4 (8) 58MB classicbeta:      6.0.4 (8) 58MB classicedge:      6.0.4 (8) 58MB classic

Roll back to a previous version of an application

Use snap revert

$ sudo snap revert <snap name>

Conclusion

By now you should be able to install snaps the store, manually update them, remove them, check installed snaps and much more. The snap command line is designed to be as simple and memorisable as possible. It should become a second nature to you after using it just a couple of times.