SSH limits

[Keisial]

Adriana Rodean wrote:
> Hi,
>
>
> I have some questions about ssh server and Linux, hope someone can help me :)
>
> 1.       Does Ssh server have a limit for the number of users that can connect ?
>   

You may have issues with MaxStartups if all those users try to connect
at once.
Otherwise, it should work.

> 2.       Does Ssh have restrictions about an username length? Or
> username format? We would like to use something like: foo_<GUID>
>
> ex: foo_ 5CEB80CF-150F-4ff0-8743-A6493FA200C1
>   
OpenSSH accepts them without problems.

> 3.       Does Linux have a limit of user accounts?
>   
On modern linux uid_t uses 4 bytes so you could have up to** 2^32
****(about 4.300
thousand) ****accounts.  **But to be efficient with thousands of
accounts you should store
the user database into a database instead of libnss_files. See
nsswitch.conf(5)


> 4.       Does Linux have restrictions about an username length? Or
> username format? We would like to use something like: foo_<GUID>
>
> ex: foo_ 5CEB80CF-150F-4ff0-8743-A6493FA200C1
>   
That seems to work. You may prefer to use
foo_5ceb80cf-150f-4ff0-8743-a6493fa200c1
since unix names are usually lowercase and a few apps may not like
uppercase letters.

useradd(8) only accepts usernames up to 32 characters long, so you
should create an
alternative app to add them.