Pin alpine version to 3

Update deprecated maintainer syntax
Pin packages to last version
Eneble user in the same RUN that creates it

Dockerfile

@@ -1,17 +1,21 @@
-FROM alpine:latest
-MAINTAINER b3vis
+FROM alpine:3
+LABEL maintainer="b3vis"
+
 #Install Borg & SSH
-RUN apk add openssh sshfs borgbackup supervisor
+RUN apk add --no-cache openssh=8.8_p1-r1 sshfs=3.7.2-r0 borgbackup=1.1.17-r2 supervisor=4.2.2-r2
 RUN adduser -D -u 1000 borg && \
-    mkdir /backups && \
+    passwd -u borg && \
+    mkdir -m 0700 /backups && \
     chown borg.borg /backups && \
     sed -i \
         -e 's/^#PasswordAuthentication yes$/PasswordAuthentication no/g' \
         -e 's/^PermitRootLogin without-password$/PermitRootLogin no/g' \
         /etc/ssh/sshd_config
+
 COPY supervisord.conf /etc/supervisord.conf
 COPY service.sh /usr/local/bin/service.sh
-RUN passwd -u borg
+
 EXPOSE 22
 VOLUME /etc/ssh
+
 CMD ["/usr/bin/supervisord"]