How to Change a Docker Container’s Clock Without Affecting the Host

Requirement

Customer data has a time limit; the test needs the data to be set to a specific point in time inside a Docker container without changing the host system time.

Implementation Logic

First, attempt to modify the container time directly.

<code>docker run -d -p 80:80 nginx:alpine
docker exec -it d0d1cc9d5 sh
# date -R
Fri, 25 Nov 2022 15:48:40 +0000
# date -s '2000-11-25 15:48:51'
date: can't set date: Operation not permitted
</code>

The failure is caused by Linux capabilities: changing the system clock requires the SYS_TIME capability, which is not granted to containers by default. You can add capabilities with

--cap-add

or grant all privileges with

--privileged

.

Using

--privileged

allows the time change, but it also changes the host clock, which is undesirable when other containers share the same host.

Using libfaketime

The open‑source libfaketime library can fake the system time for a single container without affecting the host.

Installation (CentOS example)

<code>FROM centos:7
RUN yum install make gcc gcc-c++ git -y && \
    git clone https://github.com/wolfcw/libfaketime && \
    cd libfaketime/src && \
    make install
ENV LD_PRELOAD=/usr/local/lib/faketime/libfaketime.so.1 \
    FAKETIME="2000-01-01 1:00:00"
ENTRYPOINT ["/usr/bin/python", "-m", "SimpleHTTPServer", "80"]
EXPOSE 80
</code>

Build and run the image:

<code>docker build -t time:centos ./
docker run --name centos -d -p 80:80 time:centos
</code>

Test 1 – Does time increase?

Access the container’s port 80 and view the logs.

<code>docker logs -f centos
192.168.199.10 - - [01/Jan/200001:00:00] "GET / HTTP/1.1" 200 -
... (repeated entries with the same timestamp)
</code>

The timestamps are fixed because

FAKETIME="2000-01-01 1:00:00"

freezes time. To make time progress, use the

@

prefix.

Update Dockerfile

<code>FROM centos:7
RUN yum install make gcc gcc-c++ git -y && \
    git clone https://github.com/wolfcw/libfaketime && \
    cd libfaketime/src && \
    make install
ENV LD_PRELOAD=/usr/local/lib/faketime/libfaketime.so.1 \
    FAKETIME="@2000-01-01 1:00:00"
ENTRYPOINT ["/usr/bin/python", "-m", "SimpleHTTPServer", "80"]
EXPOSE 80
</code>

Rebuild and run the updated image:

<code>docker build -t time:centos-v1 ./
docker run --name centos -d -p 80:80 time:centos-v1
docker logs -f centos
192.168.199.10 - - [01/Jan/200001:00:10] "GET / HTTP/1.1" 200 -
192.168.199.10 - - [01/Jan/200001:00:20] "GET / HTTP/1.1" 200 -
192.168.199.10 - - [01/Jan/200001:00:22] "GET / HTTP/1.1" 200 -
</code>

The logs now show timestamps advancing, confirming that the

@

prefix makes the fake time increase while the host clock remains unchanged.