PAM_SM_AUTHENTICATE(3)

💅 PAM_SM_AUTHENTICATE(3) — like, the Linux-PAM Manual page, bestie

okay so real talk: this is the PAM_SM_AUTHENTICATE page from the Linux-PAM Manual, and it's genuinely one of the most important ones if you're writing a PAM service module. no cap. let's get into it ✨

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🌸 NAME 🌸

pam_sm_authenticate — the PAM service function you implement for user authentication. it's THE entry point, the main character of auth modules 🫶

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🎀 SYNOPSIS 🎀

#include <security/pam_modules.h>

int pam_sm_authenticate(pam_handle_t *pamh, int flags, int argc,
                        const char **argv);

look at her. four args, returns an int. iconic signature, no notes 💅

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🦋 DESCRIPTION 🦋

so pam_sm_authenticate is literally the service module's very own implementation of the pam_authenticate(3) interface. that's the whole vibe — the app calls pam_authenticate(3), and PAM comes knocking on your module like "hey bestie, do the thing" 💖

this function performs the task of authenticating the user. that's it. that's the job. you check the credentials, you decide yes or no, and you return a status. periodt.

valid flags, which may be logically OR'd with PAM_SILENT, are:

• PAM_SILENT — do not emit any messages. like, shhh 🤫 zero chatter, zero output.
• PAM_DISALLOW_NULL_AUTHTOK — return PAM_AUTH_ERR if the database of authentication tokens for this authentication mechanism has a NULL entry for the user. and listen, this one matters: without this flag, such a NULL token will lead to a success without the user being prompted. yeah. 😭 like it just... lets them in. no prompt, no nothing. so set this flag unless you enjoy chaos 💀

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🔥 RETURN VALUES 🔥

here's your whole output menu, bestie — memorize these, they're your love language:

• PAM_AUTH_ERR — authentication failure. the classic. it didn't work, say so 💔
• PAM_CRED_INSUFFICIENT — for some reason the application does not have sufficient credentials to authenticate the user. not the user's fault, the app's just underdressed for the occasion 🙈
• PAM_AUTHINFO_UNAVAIL — the modules were not able to access the authentication information. this might be due to a network or hardware failure etc. like the info is right there and you simply cannot reach it 🫠
• PAM_SUCCESS — the authentication token was successfully updated. slay 🎉
• PAM_USER_UNKNOWN — the supplied username is not known to the authentication service. who is she? never heard of her 👑 (gently)
• PAM_MAXTRIES — one or more of the authentication modules has reached its limit of tries authenticating the user. do not try again. like seriously, stop, the door is closed, go home ⭐

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🌈 SEE ALSO 🌈

go read these next, i'm obsessed with cross-references:

• pam(3)
• pam_authenticate(3)
• pam_sm_setcred(3)
• pam_strerror(3)
• PAM(8)

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and that's the page!! mwah 💜 this one's from Linux-PAM and it was dated 07/08/2026, so like — timestamped, documented, and forever iconic. go write a gorgeous auth module bestie, you got this 🧚✨🍓