If you need to connect to the sandbox SFDX

 You can always view all possible connection methods in sfdx

sfdx auth --help 

 

 

 

if you don't have a browser, 2 methods are most often used:

1) sfdx auth:accesstoken:store (authorize an org using an existing Salesforce access token)

 

You can get a token using the command:

sfdx force:org:display -u <Alias/username>

2) sfdx auth:sfdxurl:store (authorize an org using an SFDX auth URL stored within a file)

 

      $ sfdx force:org:display -u <OrgUsername> --verbose --json > authFile.json
      $ sfdx auth:sfdxurl:store -f authFile.json  -a <Alias>

copy file (nix):

$ scp <filepath> username@ip <new file path>