$apropos 5 passwd |grep use
adduser.conf(5) - adduser(8) configuration file
audit_user(5) - events to be audited for given users
ftpusers(5), ftpchroot(5) - ftpd(8) access control file
hosts.equiv(5), .rhosts(5) - trusted remote host and user name data base
hosts.lpd(5) - trusted hosts that may use local print services
krb5_auth_context(3), krb5_auth_con_init(3), krb5_auth_con_free(3), krb5_auth_con_setflags(3), krb5_auth_con_getflags(3), krb5_auth_con_setaddrs(3), krb5_auth_con_setaddrs_from_fd(3), krb5_auth_con_getaddrs(3), krb5_auth_con_genaddrs(3), krb5_auth_con_getkey(3), krb5_auth_con_setkey(3), krb5_auth_con_getuserkey(3), krb5_auth_con_setuserkey(3), krb5_auth_con_getlocalsubkey(3), krb5_auth_con_setloca
krb5_kuserok(3) - verifies if a principal can log in as a user
krb5_verify_user(3), krb5_verify_user_lrealm(3), krb5_verify_user_opt(3), krb5_verify_opt_init krb5_verify_opt_set_flags(3), krb5_verify_opt_set_service(3), krb5_verify_opt_set_secure(3), krb5_verify_opt_set_keytab(3) - Heimdal password verifying functions
lj4_font(5) - groff fonts for use with devlj4
opiekeys(5), /etc/opiekeys(5) - OPIE database of user key information
quota.user(5), quota.group(5) - per file system quota database
gnutls_x509_crl_deinit(3) - This function deinitializes memory used by a gnutls_x509_crl_t structure
gnutls_x509_crq_deinit(3) - This function deinitializes memory used by a gnutls_x509_crq_t structure
gnutls_x509_crt_deinit(3) - This function deinitializes memory used by a gnutls_x509_crt_t structure
gnutls_x509_privkey_deinit(3) - This function deinitializes memory used by a gnutls_x509_privkey_t structure
sudoers(5) - list of which users may execute what
gnutls_x509_crl_deinit(3) - This function deinitializes memory used by a gnutls_x509_crl_t structure
gnutls_x509_crq_deinit(3) - This function deinitializes memory used by a gnutls_x509_crq_t structure
gnutls_x509_crt_deinit(3) - This function deinitializes memory used by a gnutls_x509_crt_t structure
gnutls_x509_privkey_deinit(3) - This function deinitializes memory used by a gnutls_x509_privkey_t structure
sudoers(5) - list of which users may execute what
opiepasswd(1) - Change or set a user's password for the OPIE authentication system
passwd(1), yppasswd(1) - modify a user's password
SSL_CTX_set_default_passwd_cb(3), SSL_CTX_set_default_passwd_cb_userdata(3) - set passwd callback for encrypted PEM file handling