Adding/editing entry in /etc/hosts file inside azure container app.

Question

Adding/editing entry in /etc/hosts file inside azure container app.

Chandrashekar, Anil (Cognizant) 40

Hi

I would like add some ip & corresponding hostname entries to /etc/hosts file within my azure container app. While i was able to do it using 'Debug console', these entries are vanished when container is redeployed and i will have to add these entries again which is cumbersome.

Is there any permanent solution(Dockerfile or any other configurable approach) to this problem where in /etc/hosts entries are not vanished when container are redeployed?

Thanks in advance.

Marcin Policht 44,360 Reputation points MVP

2025-04-01T22:45:33.9733333+00:00
Try either of the following:

1. Modify the Dockerfile (if you control the container image) You can modify /etc/hosts during the container build process by adding a command in your Dockerfile:

RUN echo "192.168.1.100 mycustomhost" >> /etc/hosts

This works only if you control the container image and can modify the Dockerfile. Plus this doesn't support dynamic updates based on deployment environments.

2. Use a startup script Use an entrypoint script to update /etc/hosts at container startup:

Example: startup.sh

#!/bin/sh echo "192.168.1.100 mycustomhost" >> /etc/hosts exec "$@"

Modify the Dockerfile to use the script

COPY startup.sh /usr/local/bin/startup.sh RUN chmod +x /usr/local/bin/startup.sh ENTRYPOINT ["/usr/local/bin/startup.sh"]

This persists even if the container is restarted. It's also easier to manage than modifying the Dockerfile directly.

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin
Shireesha Eeraboina 2,815 Reputation points Microsoft External Staff

2025-04-03T05:20:02.1466667+00:00

Hello Chandrashekar, Anil (Cognizant),

Just checking in to see if the above answer provided by @Marcin Policht helped.

if you have any further query do let us know.
Chandrashekar, Anil (Cognizant) 40 Reputation points

2025-04-03T13:24:53.55+00:00

Hi Marcin & Shireesha

I tried the same approach and i don't see the hosts entries added in the container etc/hosts file. I have added this as separate entry point in my dockerfile along with the one existing.

Something like the below.

COPY startup.sh /usr/local/bin/startup.sh

RUN chmod +x /usr/local/bin/startup.sh

ENTRYPOINT ["/usr/local/bin/startup.sh"]

ENTRYPOINT ["abc","xyz"]
Marcin Policht 44,360 Reputation points MVP

2025-04-03T14:18:40.9666667+00:00
Verify that the startup.sh script looks like the following (adjust accordingly)

#!/bin/sh echo "192.168.1.100 mycustomhost" >> /etc/hosts exec "$@"

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin
Chandrashekar, Anil (Cognizant) 40 Reputation points

2025-04-03T16:28:48.1466667+00:00

Hi Marcin

This is exactly the same syntax i have in my startup.sh. Unfortunately entries are not getting added to /etc/hosts. Is there a way to debug this?
Marcin Policht 44,360 Reputation points MVP

2025-04-03T21:46:34.0266667+00:00
Your issue is caused by having multiple ENTRYPOINT directives in your Dockerfile. Only the last ENTRYPOINT takes effect, which overrides your startup script. Instead of using two ENTRYPOINT directives, modify your script so it executes your main process after updating /etc/hosts. Here’s how:

1. Modify startup.sh Ensure your script updates /etc/hosts and then executes the main process:

#!/bin/sh echo "192.168.1.100 mycustomhost" >> /etc/hosts exec "$@" # This runs the main container process

2. Modify Dockerfile Set the startup script as the ENTRYPOINT and pass the main process as arguments.

COPY startup.sh /usr/local/bin/startup.sh RUN chmod +x /usr/local/bin/startup.sh ENTRYPOINT ["/usr/local/bin/startup.sh"] CMD ["abc", "xyz"] # This is the main process that gets executed after startup.sh

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin
Chandrashekar, Anil (Cognizant) 40 Reputation points

2025-04-04T19:57:42.3766667+00:00

Hi Marcin

Tried as you suggested above and received below error when i ran it in my Docker Desktop.

2025-04-04 14:43:12 exec /usr/local/bin/startup.sh: no such file or directory
Marcin Policht 44,360 Reputation points MVP

2025-04-04T21:52:32.6033333+00:00
This might be caused by a number of things - such as:

Wrong line endings (Windows vs Unix) If you're building on Windows, your startup.sh file might have CRLF line endings (carriage return + line feed), which Linux doesn't like.

Convert the script to Unix line endings (LF):

In VS Code: Bottom-right corner > Click on CRLF > Select LF.

Or run this on WSL/Linux/macOS:
dos2unix startup.sh

File not copied correctly Double-check that the COPY instruction in the Dockerfile is correct and matches the path.

Example Dockerfile:

# Base image FROM ubuntu:latest # Copy startup script COPY startup.sh /usr/local/bin/startup.sh # Set permissions RUN chmod +x /usr/local/bin/startup.sh # Set entrypoint ENTRYPOINT ["/usr/local/bin/startup.sh"]

Make sure startup.sh is in the same folder as your Dockerfile, or adjust the COPY path.

Interpreter missing (e.g., #!/bin/sh or #!/bin/bash) Check the first line of your script. It must start with a proper shebang (interpreter directive):

#!/bin/sh

or

#!/bin/bash

And ensure that /bin/sh or /bin/bash actually exists in your base image (e.g., Alpine uses /bin/sh, not Bash).

To debug in the Dockerfile, add this temporarily to your Dockerfile before the ENTRYPOINT:

RUN ls -l /usr/local/bin/startup.sh && head -n 1 /usr/local/bin/startup.sh && file /usr/local/bin/startup.sh

It'll give you insight into:

Whether the file exists

What the first line looks like (to see the shebang)

If it has Windows line endings (with CRLF line terminators)

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin
Shireesha Eeraboina 2,815 Reputation points Microsoft External Staff

2025-04-07T05:39:17.31+00:00

Hello Chandrashekar, Anil (Cognizant),

Just checking in to see if above information was helpful. If you have any further updates on this issue, please feel free to post back
Chandrashekar, Anil (Cognizant) 40 Reputation points

2025-04-07T23:29:07.23+00:00
Here is my Dockerfile.

FROM openjdk:17 COPY startup.sh /usr/local/bin/startup.sh RUN chmod +x /usr/local/bin/startup.sh RUN ls -l /usr/local/bin/startup.sh && head -n 1 /usr/local/bin/startup.sh && file /usr/local/bin/startup.sh ENTRYPOINT ["/usr/local/bin/startup.sh"] CMD ["java","-jar","abc.jar"]

and it errored out(below error) during docker image build. Looks like above commands are only applicable for ubuntu image?

=> ERROR [10/10] RUN ls -l /usr/local/bin/startup.sh && head -n 1 /usr/local/bin/startup.sh && file /usr/local/bin/startup.sh 0.8s ------ > [10/10] RUN ls -l /usr/local/bin/startup.sh && head -n 1 /usr/local/bin/startup.sh && file /usr/local/bin/startup.sh: 0.714 -rwxr-xr-x 1 root root 87 Apr 4 19:07 /usr/local/bin/startup.sh 0.717 #!/bin/sh 0.718 /bin/sh: file: command not found
Shireesha Eeraboina 2,815 Reputation points Microsoft External Staff

2025-04-09T03:46:23.96+00:00

Hi Chandrashekar, Anil (Cognizant),

Just checking in to see if above information was helpful. If you have any further updates on this issue, please feel free to post back.
Shireesha Eeraboina 2,815 Reputation points Microsoft External Staff

2025-04-10T05:19:55.24+00:00

Hello Chandrashekar, Anil (Cognizant) ,

Following up to see if you had a chance to review the above response. If you have any further updates on this issue, please feel free to post them here.
Chandrashekar, Anil (Cognizant) 40 Reputation points

2025-04-10T22:46:36.11+00:00

Hi Shireesha

For some reason it didn't work for me. startup.sh was unable to be copied to the path specified in docker desktop and received below error.

2025-04-04 14:43:12 exec /usr/local/bin/startup.sh: no such file or directory
Chandrashekar, Anil (Cognizant) 40 Reputation points

2025-04-11T15:08:53.15+00:00

Thank you Shireesha & Marcin. This is working now. Really appreciate your help.
Marcin Policht 44,360 Reputation points MVP

2025-04-11T17:06:30.2+00:00

You are welcome. Pls mark the response accordingly.

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin

Accepted answer

1 additional answer

Your answer

Marcin Policht 44,360 Reputation points MVP

2025-04-01T22:45:33.9733333+00:00

Try either of the following:

1. Modify the Dockerfile (if you control the container image) You can modify /etc/hosts during the container build process by adding a command in your Dockerfile:

RUN echo "192.168.1.100 mycustomhost" >> /etc/hosts

This works only if you control the container image and can modify the Dockerfile. Plus this doesn't support dynamic updates based on deployment environments.

2. Use a startup script Use an entrypoint script to update /etc/hosts at container startup:

Example: startup.sh

#!/bin/sh echo "192.168.1.100 mycustomhost" >> /etc/hosts exec "$@"

Modify the Dockerfile to use the script

COPY startup.sh /usr/local/bin/startup.sh RUN chmod +x /usr/local/bin/startup.sh ENTRYPOINT ["/usr/local/bin/startup.sh"]

This persists even if the container is restarted. It's also easier to manage than modifying the Dockerfile directly.

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin
Shireesha Eeraboina 2,815 Reputation points Microsoft External Staff

2025-04-03T05:20:02.1466667+00:00

Hello Chandrashekar, Anil (Cognizant),

Just checking in to see if the above answer provided by @Marcin Policht helped.

if you have any further query do let us know.
Chandrashekar, Anil (Cognizant) 40 Reputation points

2025-04-03T13:24:53.55+00:00

Hi Marcin & Shireesha

I tried the same approach and i don't see the hosts entries added in the container etc/hosts file. I have added this as separate entry point in my dockerfile along with the one existing.

Something like the below.

COPY startup.sh /usr/local/bin/startup.sh

RUN chmod +x /usr/local/bin/startup.sh

ENTRYPOINT ["/usr/local/bin/startup.sh"]

ENTRYPOINT ["abc","xyz"]
Marcin Policht 44,360 Reputation points MVP

2025-04-03T14:18:40.9666667+00:00

Verify that the startup.sh script looks like the following (adjust accordingly)

#!/bin/sh echo "192.168.1.100 mycustomhost" >> /etc/hosts exec "$@"

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin
Chandrashekar, Anil (Cognizant) 40 Reputation points

2025-04-03T16:28:48.1466667+00:00

Hi Marcin

This is exactly the same syntax i have in my startup.sh. Unfortunately entries are not getting added to /etc/hosts. Is there a way to debug this?
Marcin Policht 44,360 Reputation points MVP

2025-04-03T21:46:34.0266667+00:00

Your issue is caused by having multiple ENTRYPOINT directives in your Dockerfile. Only the last ENTRYPOINT takes effect, which overrides your startup script. Instead of using two ENTRYPOINT directives, modify your script so it executes your main process after updating /etc/hosts. Here’s how:

1. Modify startup.sh Ensure your script updates /etc/hosts and then executes the main process:

#!/bin/sh echo "192.168.1.100 mycustomhost" >> /etc/hosts exec "$@" # This runs the main container process

2. Modify Dockerfile Set the startup script as the ENTRYPOINT and pass the main process as arguments.

COPY startup.sh /usr/local/bin/startup.sh RUN chmod +x /usr/local/bin/startup.sh ENTRYPOINT ["/usr/local/bin/startup.sh"] CMD ["abc", "xyz"] # This is the main process that gets executed after startup.sh

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin
Chandrashekar, Anil (Cognizant) 40 Reputation points

2025-04-04T19:57:42.3766667+00:00

Hi Marcin

Tried as you suggested above and received below error when i ran it in my Docker Desktop.

2025-04-04 14:43:12 exec /usr/local/bin/startup.sh: no such file or directory
Marcin Policht 44,360 Reputation points MVP

2025-04-04T21:52:32.6033333+00:00

This might be caused by a number of things - such as:

Wrong line endings (Windows vs Unix) If you're building on Windows, your startup.sh file might have CRLF line endings (carriage return + line feed), which Linux doesn't like.

Convert the script to Unix line endings (LF):

In VS Code: Bottom-right corner > Click on CRLF > Select LF.

Or run this on WSL/Linux/macOS:
dos2unix startup.sh

File not copied correctly Double-check that the COPY instruction in the Dockerfile is correct and matches the path.

Example Dockerfile:

# Base image FROM ubuntu:latest # Copy startup script COPY startup.sh /usr/local/bin/startup.sh # Set permissions RUN chmod +x /usr/local/bin/startup.sh # Set entrypoint ENTRYPOINT ["/usr/local/bin/startup.sh"]

Make sure startup.sh is in the same folder as your Dockerfile, or adjust the COPY path.

Interpreter missing (e.g., #!/bin/sh or #!/bin/bash) Check the first line of your script. It must start with a proper shebang (interpreter directive):

#!/bin/sh

or

#!/bin/bash

And ensure that /bin/sh or /bin/bash actually exists in your base image (e.g., Alpine uses /bin/sh, not Bash).

To debug in the Dockerfile, add this temporarily to your Dockerfile before the ENTRYPOINT:

RUN ls -l /usr/local/bin/startup.sh && head -n 1 /usr/local/bin/startup.sh && file /usr/local/bin/startup.sh

It'll give you insight into:

Whether the file exists

What the first line looks like (to see the shebang)

If it has Windows line endings (with CRLF line terminators)

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin
Shireesha Eeraboina 2,815 Reputation points Microsoft External Staff

2025-04-07T05:39:17.31+00:00

Hello Chandrashekar, Anil (Cognizant),

Just checking in to see if above information was helpful. If you have any further updates on this issue, please feel free to post back
Chandrashekar, Anil (Cognizant) 40 Reputation points

2025-04-07T23:29:07.23+00:00

Here is my Dockerfile.

FROM openjdk:17 COPY startup.sh /usr/local/bin/startup.sh RUN chmod +x /usr/local/bin/startup.sh RUN ls -l /usr/local/bin/startup.sh && head -n 1 /usr/local/bin/startup.sh && file /usr/local/bin/startup.sh ENTRYPOINT ["/usr/local/bin/startup.sh"] CMD ["java","-jar","abc.jar"]

and it errored out(below error) during docker image build. Looks like above commands are only applicable for ubuntu image?

=> ERROR [10/10] RUN ls -l /usr/local/bin/startup.sh && head -n 1 /usr/local/bin/startup.sh && file /usr/local/bin/startup.sh 0.8s ------ > [10/10] RUN ls -l /usr/local/bin/startup.sh && head -n 1 /usr/local/bin/startup.sh && file /usr/local/bin/startup.sh: 0.714 -rwxr-xr-x 1 root root 87 Apr 4 19:07 /usr/local/bin/startup.sh 0.717 #!/bin/sh 0.718 /bin/sh: file: command not found
Shireesha Eeraboina 2,815 Reputation points Microsoft External Staff

2025-04-09T03:46:23.96+00:00

Hi Chandrashekar, Anil (Cognizant),

Just checking in to see if above information was helpful. If you have any further updates on this issue, please feel free to post back.
Shireesha Eeraboina 2,815 Reputation points Microsoft External Staff

2025-04-10T05:19:55.24+00:00

Hello Chandrashekar, Anil (Cognizant) ,

Following up to see if you had a chance to review the above response. If you have any further updates on this issue, please feel free to post them here.
Chandrashekar, Anil (Cognizant) 40 Reputation points

2025-04-10T22:46:36.11+00:00

Hi Shireesha

For some reason it didn't work for me. startup.sh was unable to be copied to the path specified in docker desktop and received below error.

2025-04-04 14:43:12 exec /usr/local/bin/startup.sh: no such file or directory
Chandrashekar, Anil (Cognizant) 40 Reputation points

2025-04-11T15:08:53.15+00:00

Thank you Shireesha & Marcin. This is working now. Really appreciate your help.
Marcin Policht 44,360 Reputation points MVP

2025-04-11T17:06:30.2+00:00

You are welcome. Pls mark the response accordingly.

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin

Answer 1

This just means that the file utility isn't installed. You can ignore it, this was just a debug helper.

Try the following

FROM openjdk:17
# Copy startup script
COPY startup.sh /usr/local/bin/startup.sh
# Make it executable
RUN chmod +x /usr/local/bin/startup.sh
# Set entrypoint and default command
ENTRYPOINT ["/usr/local/bin/startup.sh"]
CMD ["java", "-jar", "abc.jar"]

where startup.sh contains something like the following:

#!/bin/sh
echo "192.168.1.100 mycustomhost" >> /etc/hosts
exec "$@"

If the above response helps answer your question, remember to "Accept Answer" so that others in the community facing similar issues can easily find the solution. Your contribution is highly appreciated.

hth

Marcin

Answer 2

Hi Chandrashekar, Anil (Cognizant),

Thanks for all the detailed updates!

Hi, the issue you're seeing is likely due to your startup.sh script having Windows-style line endings (CRLF), which Linux containers can't read.

Please change the line endings to Unix (LF) — in VS Code, just click on "CRLF" at the bottom right and select "LF", or use dos2unix startup.sh.

Also, make sure the script is in the same folder as your Dockerfile and starts with #!/bin/sh. In your Dockerfile, use only one ENTRYPOINT, like this: ENTRYPOINT ["/usr/local/bin/startup.sh"], and define your app command with CMD. This should fix the "no such file or directory" error and allow the hosts entry to be added properly.

For your reference, please review the following documentations for further clarification:

https://stackoverflow.com/questions/29535015/error-cannot-start-container-stat-bin-sh-no-such-file-or-directory

https://forums.docker.com/t/standard-init-linux-go-exec-user-process-caused-no-such-file-or-directory/35691

I hope this addresses your query. Please let me know if you need any further assistance or clarification.

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Adding/editing entry in /etc/hosts file inside azure container app.

1 additional answer

Your answer