I would write “Log in to host.com.”
I think that “login” is a noun (as in “login screen”).
I would find the words “loginned” and “loginning” awkward.
As for “Log in to host.com” versus “Log into host.com,” I would use the former because I think that “log in” is a fixed phrase.
Martha’s answer to another question is also related.
Added :
The Corpus of Contemporary American English (COCA) lists 65 occurrences of “log in to” and 58 occurrences of “log into,” both including inflected forms and excluding the Spoken section.
(The queries used are [log].[v*] in to and [log].[v*] into .)
Since “log in to” is also used in context like “log in to download it,” the actual number of occurrences of “log in to [host]” is slightly smaller than 65.
In any case, it suggests that the phrase “log into” is also used commonly, although I am not sure how good it is to use COCA to compare technical terms.
english.stackexchange.com/users/1755/Tsuyoshi Ito
The verb is log in .
Log in to host.com From the Wikipedia page for Login :
Spelling confusion
The verbs are two words: log in and log out , whereas the nouns are login and logout (often used like adjectives in compound nouns).
english.stackexchange.com/users/212/b.roth
Yes, I agree: Use " log in to " as a verb.
So use that for givinginstructions.
" log into " is not terrible, but it doesn't sound as good because itsounds like you're actually going inside something.
For example, "Iwalked into the store." " login " is the noun and adjective form.
So you would use that likethis: "I programmed the login procedure.
"
Or... "I don't like thisapp because the login process is very lengthy."
You can also think about each one with the way we stress the different syllables slightly when we're speaking: "log in to host.com" sounds like " log + in + to host.com"
(each word is pretty much evenly stressed) "log into host.com" sounds like " log + INto host.com"
(the stress is on "in") "login to host.com"
sounds like " LOGin + to host.com"
(the stress is on "log")
english.stackexchange.com/users/33304/Dave
Ironic that the instruction at the bottom of this page is 'Sign up or login'.
I'm here because I'm torn between log in to and log into and looking for clarification.
At this point in time, I suspect the prevailing opinion is correct - that log in to is preferable for purposes of clarity.
However, I don't doubt that we will soon treat the process of logging in as a figurative point of entry, meaning that log into will make full conceptual sense (cf you don't physically delve into a problem or pile into an argument, yet both are correct grammatically because they are semantically [i.e. figuratively]).
english.stackexchange.com/users/63114/Richard
Given that so much of the web environment isn't being written by writers who care, I'm increasingly seeing 'login' used as a verb.
And to be honest, once it's normalised it will be the correct form.
I'm a digital copywriter and have fought this battle on a few occasions.
But I've decided to throw in my hand. '
Login to this site'. '
Enter your login details'.
Fine, whatever.
Is it clear?
Absolutely.
Only people like us care.
english.stackexchange.com/users/79968/Simon G
When writing an instruction about connecting to a computer using ssh, telnet, etc., I'm not sure what spacing to use in this familiar spoken phrase:   " Log in to  host.com"  " Log into  host.com"  " Login to  host.com"   Maybe this is entirely subjective or the realm of industry jargon, but I couldn't think of anywhere else to ask.  Any insight?
"log in to" or "log into" or "login to"
english.stackexchange.com
<verbs><terminology><orthography><phrasal-verbs><programming>
english.stackexchange.com/questions/5302
english.stackexchange.com/users/198/John Siracusa
Of the three options, it appears that "log in to" is the preferred option, although, "log into" is not terrible. Log in to host.com is the correct form. "Login" as a single verb seems awkward, it would imply past tens of "loginned" for example.The COCA has variant occurrences for "log in to" and "log into". Log into is not awful, but not as good because it sounds you are going inside something. It is likely that "log in" in the future will become a form of speech to indicate a figurative point of entry.
Of the three options, it appears that "log in to" is the preferred option, although, "log into" is not terrible. Login' is increasingly being used as a verb online, but the verb is  actually log in .  The verbs are two words:  log in  and   log out , whereas the nouns are  login   and  logout  (often used like adjectives  in compound nouns).  
As the verb is "to log in", many people suggest "log in to", although "log into" is not considered to be terrible. Of the three options, it appears that "log in to" is the preferred option, although, "log into" may be acceptable to some people.
"Log in to host.com" is the correct form. "Login" as a single verb seems awkward, it would imply past tens of "loginned" for example. The COCA has variant occurrences for "log in to" and "log into". Log into is not awful, but not as good because it sounds you are going inside something. It is likely that "log in" in the future will become a form of speech to indicate a figurative point of entry.
Login' is increasingly being used as a verb online. The verb is  log in .    The verbs are two words:  log in  and   log out , whereas the nouns are  login   and  logout  (often used like adjectives  in compound nouns).  
Of the three options, there appears to be a preference for "log in to", with three separate words. The phrase "log into" may be acceptable to some people.