diff --git a/services/upgrader/pubkey.gpg b/services/upgrader/pubkey.gpg
new file mode 100644
index 0000000000..173374ebda
--- /dev/null
+++ b/services/upgrader/pubkey.gpg
@@ -0,0 +1,18 @@
+-----BEGIN PGP PUBLIC KEY BLOCK-----
+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+=kkvg
+-----END PGP PUBLIC KEY BLOCK-----
diff --git a/services/upgrader/upgrader_linux.go b/services/upgrader/upgrader_linux.go
index 0cb2b6c881..fa45dd4951 100644
--- a/services/upgrader/upgrader_linux.go
+++ b/services/upgrader/upgrader_linux.go
@@ -7,6 +7,7 @@ import (
 	"archive/tar"
 	"bytes"
 	"compress/gzip"
+	_ "embed"
 	"fmt"
 	"io"
 	"io/ioutil"
@@ -17,6 +18,7 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"sync"
 	"sync/atomic"
 	"syscall"
 
@@ -27,48 +29,65 @@ import (
 	"github.com/mattermost/mattermost-server/v6/shared/mlog"
 )
 
-const mattermostBuildPublicKey = `-----BEGIN PGP PUBLIC KEY BLOCK-----
+//go:embed pubkey.gpg
+var mattermostBuildPublicKeys []byte
 
-mQENBFjZQxwBCAC6kNn3zDlq/aY83M9V7MHVPoK2jnZ3BfH7sA+ibQXsijCkPSR4
-5bCUJ9qVA4XKGK+cpO9vkolSNs10igCaaemaUZNB6ksu3gT737/SZcCAfRO+cLX7
-Q2la+jwTvu1YeT/M5xDZ1KHTFxsGskeIenz2rZHeuZwBl9qep34QszWtRX40eRts
-fl6WltLrepiExTp6NMZ50k+Em4JGM6CWBMo22ucy0jYjZXO5hEGb3o6NGiG+Dx2z
-b2J78LksCKGsSrn0F1rLJeA933bFL4g9ozv9asBlzmpgG77ESg6YE1N/Rh7WDzVA
-prIR0MuB5JjElASw5LDVxDV6RZsxEVQr7ETLABEBAAG0KU1hdHRlcm1vc3QgQnVp
-bGQgPGRldi1vcHNAbWF0dGVybW9zdC5jb20+iQFUBBMBCAA+AhsDBQsJCAcCBhUI
-CQoLAgQWAgMBAh4BAheAFiEEobMdRvDzoQsCzy1E+PLDF0R3SygFAmJOqWgFCQ03
-zUwACgkQ+PLDF0R3Syg/rQf8D5BgvVFnGuHDYNu2eiasZdfxmuhg1C7JGSLHqoCT
-SB/0SLLQyMeHsJLye/gbo3yhK8G9XYOm+obGF+NDxB0LtRaPv5Q6pIQYt88ZxOGA
-Kh6RG2DjYA5j410wYrN0mNzhudqnS2yZdyq215nEr7Z6l1T7L9OPcz0u0mF9RraQ
-nawzxbxc8mPuC5tMLTedViSkTYLgMY12TCSYhykseUIGrl/FBfMbmKwBHM52SZJh
-maBevuNymlFbODTciyE9Q7mJHkaamGKTXaa3Enlcf16oSoemawSBJuspaS0sZOW8
-dgi5l3V5YvfFvSk45axiZbnGYfN81G5mkSGAENSGSKVtMA==
-=kkvg
------END PGP PUBLIC KEY BLOCK-----`
-
-var upgradePercentage int64
-var upgradeError error
-var upgrading int32
+var (
+	upgradePercentage int64
+	m                 sync.Mutex
+	upgradeError      error
+	upgrading         int32
+)
 
 type writeCounter struct {
-	total  int64
-	readed int64
+	total int64
+	read  int64
 }
 
 func (wc *writeCounter) Write(p []byte) (int, error) {
 	n := len(p)
-	wc.readed += int64(n)
-	percentage := (wc.readed * 100) / wc.total
-	if percentage == 0 {
-		upgradePercentage = 1
-	} else if percentage == 100 {
-		upgradePercentage = 99
-	} else {
-		upgradePercentage = percentage
+	wc.read += int64(n)
+
+	if wc.total <= 0 {
+		// skip the percentage calculation for invalid totals
+		setUpgradePercentage(50)
+		return n, nil
 	}
+
+	percentage := (wc.read * 100) / wc.total
+	if percentage == 0 {
+		percentage = 1
+	} else if percentage >= 100 {
+		percentage = 99
+	}
+
+	setUpgradePercentage(percentage)
+
 	return n, nil
 }
 
+func getUpgradePercentage() int64 {
+	return atomic.LoadInt64(&upgradePercentage)
+}
+
+func setUpgradePercentage(to int64) {
+	atomic.StoreInt64(&upgradePercentage, to)
+}
+
+func getUpgradeError() error {
+	m.Lock()
+	defer m.Unlock()
+
+	return upgradeError
+}
+
+func setUpgradeError(err error) {
+	m.Lock()
+	defer m.Unlock()
+
+	upgradeError = err
+}
+
 func getCurrentVersionTgzURL() string {
 	version := model.CurrentVersion
 	if strings.HasPrefix(model.BuildNumber, version+"-rc") {
@@ -78,8 +97,8 @@ func getCurrentVersionTgzURL() string {
 	return "https://releases.mattermost.com/" + version + "/mattermost-" + version + "-linux-amd64.tar.gz"
 }
 
-func verifySignature(filename string, sigfilename string, publicKey string) error {
-	keyring, err := openpgp.ReadArmoredKeyRing(bytes.NewReader([]byte(publicKey)))
+func verifySignature(filename string, sigfilename string, publicKey []byte) error {
+	keyring, err := openpgp.ReadArmoredKeyRing(bytes.NewReader(publicKey))
 	if err != nil {
 		mlog.Debug("Unable to load the public key to verify the file signature", mlog.Err(err))
 		return NewInvalidSignature()
@@ -173,14 +192,14 @@ func UpgradeToE0() error {
 	}
 	defer atomic.CompareAndSwapInt32(&upgrading, 1, 0)
 
-	upgradePercentage = 1
-	upgradeError = nil
+	setUpgradePercentage(1)
+	setUpgradeError(nil)
 
 	executablePath, err := os.Executable()
 	if err != nil {
-		upgradePercentage = 0
-		upgradeError = errors.New("error getting the executable path")
+		setUpgradeError(errors.New("error getting the executable path"))
 		mlog.Error("Unable to get the path of the Mattermost executable", mlog.Err(err))
+		setUpgradePercentage(0)
 		return err
 	}
 
@@ -189,9 +208,9 @@ func UpgradeToE0() error {
 		if filename != "" {
 			os.Remove(filename)
 		}
-		upgradeError = fmt.Errorf("error downloading the new Mattermost server binary file (percentage: %d)", upgradePercentage)
-		mlog.Error("Unable to download the Mattermost server binary file", mlog.Int64("percentage", upgradePercentage), mlog.String("url", getCurrentVersionTgzURL()), mlog.Err(err))
-		upgradePercentage = 0
+		setUpgradeError(fmt.Errorf("error downloading the new Mattermost server binary file (percentage: %d)", getUpgradePercentage()))
+		mlog.Error("Unable to download the Mattermost server binary file", mlog.Int64("percentage", getUpgradePercentage()), mlog.String("url", getCurrentVersionTgzURL()), mlog.Err(err))
+		setUpgradePercentage(0)
 		return err
 	}
 	defer os.Remove(filename)
@@ -200,34 +219,35 @@ func UpgradeToE0() error {
 		if sigfilename != "" {
 			os.Remove(sigfilename)
 		}
-		upgradeError = errors.New("error downloading the signature file of the new server")
+		setUpgradeError(errors.New("error downloading the signature file of the new server"))
 		mlog.Error("Unable to download the signature file of the new Mattermost server", mlog.String("url", getCurrentVersionTgzURL()+".sig"), mlog.Err(err))
-		upgradePercentage = 0
+		setUpgradePercentage(0)
 		return err
 	}
 	defer os.Remove(sigfilename)
 
-	err = verifySignature(filename, sigfilename, mattermostBuildPublicKey)
+	err = verifySignature(filename, sigfilename, mattermostBuildPublicKeys)
 	if err != nil {
-		upgradePercentage = 0
-		upgradeError = errors.New("unable to verify the signature of the downloaded file")
+		setUpgradeError(errors.New("unable to verify the signature of the downloaded file"))
 		mlog.Error("Unable to verify the signature of the downloaded file", mlog.Err(err))
+		setUpgradePercentage(0)
 		return err
 	}
 
 	err = extractBinary(executablePath, filename)
 	if err != nil {
-		upgradePercentage = 0
-		upgradeError = err
+		setUpgradeError(err)
 		mlog.Error("Unable to extract the binary from the downloaded file", mlog.Err(err))
+		setUpgradePercentage(0)
 		return err
 	}
-	upgradePercentage = 100
+
+	setUpgradePercentage(100)
 	return nil
 }
 
 func UpgradeToE0Status() (int64, error) {
-	return upgradePercentage, upgradeError
+	return getUpgradePercentage(), getUpgradeError()
 }
 
 func download(url string, limit int64) (string, error) {