Modify Docker Container Time Independently of the Host System

Requirement

The client provides data with a time constraint and needs to test it at a specific timestamp without altering the host machine’s clock.

Host OS: CentOS Linux release 7.7.1908 (Core)

Implementation Logic

First, try to change the container’s time directly:

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
Fri Nov 25 15:48:51 UTC 2022

The date command fails because Docker isolates containers using Linux capabilities; modifying system time requires the SYS_TIME capability. Adding --cap-add, dropping capabilities with --cap-drop, or using --privileged can grant or restrict such permissions. The --privileged flag gives the container all capabilities.

Using --privileged to change time:

docker run --name ngx -d -p 80:80 --privileged nginx:alpine
docker exec -it ngx sh
# date
Fri Nov 25 15:57:09 UTC 2022
# date -s '2000-11-25 15:57:14'
Sat Nov 25 15:57:14 UTC 2000
# date -R
Sat, 25 Nov 2000 15:57:17 +0000

Time inside the container changes, and the host’s clock is also altered, which is undesirable when only the container should be affected.

Solution: use the open‑source libfaketime library to fake time inside a single container.

Installation Process (CentOS example)

Create a Dockerfile:

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

Build the image: docker build -t time:centos ./ Run the container:

docker run --name centos -d -p 80:80 time:centos

Test 1 – Does Time Increment?

Access port 80 via a browser and view the container logs:

docker logs -f centos
192.168.199.10 - - [01/Jan/2000 01:00:00] "GET / HTTP/1.1" 200 -
... (repeated entries) ...

The timestamps remain fixed, showing that time does not advance when FAKETIME="2000-01-01 1:00:00" is used.

To make time progress, set FAKETIME="@2000-01-01 1:00:00" instead.

Update the Dockerfile:

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

Rebuild and run:

docker build -t time:centos-v1 ./
docker run --name centos -d -p 80:80 time:centos-v1

Check logs again:

docker logs -f centos
192.168.199.10 - - [01/Jan/2000 01:00:10] "GET / HTTP/1.1" 200 -
192.168.199.10 - - [01/Jan/2000 01:00:20] "GET / HTTP/1.1" 200 -
192.168.199.10 - - [01/Jan/2000 01:00:22] "GET / HTTP/1.1" 200 -

The timestamps now increase, confirming the effect of the leading @ in FAKETIME .

Reference link: https://www.cnblogs.com/hukey/p/16926000.html (copyright belongs to the original author).