[mod] script to build & install a redis instance

A script to build & install a simple & isolated redis service, dedicated to
SearXNG and connected via Unix socket.

    $ ./manage redis.help
    redis.:
      devpkg    : install essential packages to compile redis
      build     : build redis binaries at /800GBPCIex4/share/SearXNG/dist/redis/6.2.6/amd64
      install   : create user (searxng-redis) and install systemd service (searxng-redis)
      remove    : delete user (searxng-redis) and remove service (searxng-redis)
      shell     : start bash interpreter from user searxng-redis
      src       : clone redis source code to <path> and checkput 6.2.6
      useradd   : create user (searxng-redis) at /usr/local/searxng-redis
      userdel   : delete user (searxng-redis)
      addgrp    : add <user> to group (searxng-redis)
      rmgrp     : remove <user> from group (searxng-redis)

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

utils/templates/lib/systemd/system/searxng-redis.service

@@ -0,0 +1,42 @@
+[Unit]
+
+Description=SearXNG redis service
+After=syslog.target
+After=network.target
+Documentation=https://redis.io/documentation
+
+[Service]
+
+Type=simple
+User=${REDIS_USER}
+Group=${REDIS_USER}
+WorkingDirectory=${REDIS_HOME}
+Restart=always
+TimeoutStopSec=0
+
+Environment=USER=${REDIS_USER} HOME=${REDIS_HOME}
+ExecStart=${REDIS_HOME_BIN}/redis-server ${REDIS_CONF}
+ExecPaths=${REDIS_HOME_BIN}
+
+LimitNOFILE=65535
+NoNewPrivileges=true
+PrivateDevices=yes
+
+# ProtectSystem=full
+ProtectHome=yes
+ReadOnlyDirectories=/
+ReadWritePaths=-${REDIS_HOME}/run
+
+UMask=007
+PrivateTmp=yes
+
+MemoryDenyWriteExecute=true
+ProtectKernelModules=true
+ProtectKernelTunables=true
+ProtectControlGroups=true
+RestrictRealtime=true
+RestrictNamespaces=true
+
+[Install]
+
+WantedBy=multi-user.target