diff --git a/Dockerfile b/Dockerfile
index fc6feb07..6061d476 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -7,10 +7,13 @@ FROM ubuntu:20.04
 
 ########################## BEGIN INSTALLATION #########################
 
-ENV NUM_CPUS=6
+ENV NUM_CPUS=1
 
 ENV TZ=UTC
 
+# Clean up package manager
+RUN apt-get clean autoclean
+
 RUN export DEBIAN_FRONTEND="noninteractive" && apt-get update && apt-get install -y --fix-missing \
     autoconf \
     automake \
@@ -66,6 +69,9 @@ RUN echo "===> Install pyenv Python 3.10" && \
 
 ########################## KALDI INSTALLATION #########################
 
+# Clean up package manager
+RUN apt-get clean autoclean
+
 RUN echo "===> Install Python 2.7 for Kaldi" && \
     add-apt-repository universe && \
     apt-get update && apt-get install -y  \
@@ -111,11 +117,14 @@ RUN ./extras/install_srilm.sh
 RUN chmod +x env.sh && \
     source ./env.sh
 
-RUN apt-get install -y libssl-dev libsqlite3-dev libbz2-dev
+RUN apt-get update && apt-get install -y libssl-dev libsqlite3-dev libbz2-dev
 
 
 ########################## DEV HELPERS INSTALLATION ####################
 
+# Clean up package manager
+RUN apt-get clean autoclean
+
 WORKDIR /tmp
 
 RUN echo "===> Install dev helpers"