Memory Required for SSH-only Linux Setup

Question

I am attempting to set up a minimal Debian or CentOS installation for internal network access.

The purpose of the setup will be to allow SSH access into the rest of the internal network—that's it. It will not need to serve any other function and will have very few additional utilities installed.

For clarity, here is the primary usage scenario for the installation:

1. SSH into this machine from outside of the network.
2. SSH out from this machine to the target machine on the internal network

My questions are:

• What is the minimum amount of memory required without running into stability or performance issues?
• How much additional memory should be reserved to later harden the machine with AppArmor or other hardening agents?
• Is there another distro (Linux or BSD) that would be better suited for this kind of application?

Additional Considerations:

• The machine must run with minimal resources ( 128 MiB RAM max )
• sshuttle may be used frequently to access the machine
• The ssh server and client will be OpenSSH

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Note: A more distro-oriented version of this question was posted here: Lightweight SSH-only distro (< 128 MiB RAM)

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Answer 1

I'm pretty sure that 128 MB is more than enough if you're only going to use SSH and AppArmor. I remember Debian taking up less than 64 MB of RAM with just SSH and an Asterisk PBX started.

Edit: As of 8 June 2020, due to general software bloat, nowadays you're going to need 256 MB of RAM in order to run a barebones Linux with nothing but SSH and AppArmor. You might be able to cut down on RAM usage if you use Gentoo and build a manually configured kernel (i.e. not with genkernel).

Answer 2

If you want to run a particular mainstream distro, the minimal amount of RAM recommended for that distro is enough.

Things like OpenWRT or uCLinux can run on single megabytes of RAM, on a box like your old router from 10 years ago, still comfortably providing SSH access (usually via dropbear and busybox).