login-utils/login.1

   1 .\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
   2 .\" May be distributed under the GNU General Public License
   3 .TH LOGIN "1" "June 2012" "util-linux" "User Commands"
   4 .SH NAME
   5 login \- begin session on the system
   6 .SH SYNOPSIS
   7 .B login
   8 [
   9 .B \-p
  10 ] [
  11 .B \-h
  12 .I host
  13 ] [
  14 .B \-H
  15 ] [
  16 .B \-f
  17 .I username
  18 |
  19 .I username
  20 ]
  21 .SH DESCRIPTION
  22 .B login
  23 is used when signing onto a system.  If no argument is given,
  24 .B login
  25 prompts for the username.
  26 .PP
  27 The user is then prompted for a password, where appropriate.  Echoing
  28 is disabled to prevent revealing the password.  Only a small number
  29 of password failures are permitted before
  30 .B login
  31 exits and the communications link is severed.
  32 .PP
  33 If password aging has been enabled for the account, the user may be
  34 prompted for a new password before proceeding.  He will be forced to
  35 provide his old password and the new password before continuing.
  36 Please refer to
  37 .BR passwd (1)
  38 for more information.
  39 .PP
  40 The user and group ID will be set according to their values in the
  41 .I /etc/passwd
  42 file.  There is one exception if the user ID is zero: in this case,
  43 only the primary group ID of the account is set.  This should allow
  44 the system administrator to login even in case of network problems.
  45 The value for
  46 .BR $HOME ,
  47 .BR $USER ,
  48 .BR $SHELL ,
  49 .BR $PATH ,
  50 .BR $LOGNAME ,
  51 and
  52 .B $MAIL
  53 are set according to the appropriate fields in the password entry.
  54 .B $PATH
  55 defaults to
  56 .I /usr\:/local\:/bin:\:/bin:\:/usr\:/bin
  57 for normal users, and to
  58 .I /usr\:/local\:/sbin:\:/usr\:/local\:/bin:\:/sbin:\:/bin:\:/usr\:/sbin:\:/usr\:/bin
  59 for root, if not otherwise configured.
  60 .P
  61 The environment variable
  62 .B $TERM
  63 will be preserved, if it exists (other environment variables are
  64 preserved if the
  65 .B \-p
  66 option is given), else it will be initialized to the terminal type on your tty.
  67 .PP
  68 Then the user's shell is started.  If no shell is specified for the
  69 user in
  70 .IR /etc\:/passwd ,
  71 then
  72 .I /bin\:/sh
  73 is used.  If there is no directory specified in
  74 .IR /etc\:/passwd ,
  75 then
  76 .I /
  77 is used (the home directory is checked for the
  78 .I .hushlogin
  79 file described below).
  80 .PP
  81 If the file
  82 .I .hushlogin
  83 exists, then a "quiet" login is performed (this disables the checking
  84 of mail and the printing of the last login time and message of the
  85 day).  Otherwise, if
  86 .I /var\:/log\:/lastlog
  87 exists, the last login time is printed (and the current login is
  88 recorded).
  89 .SH OPTIONS
  90 .TP
  91 .B \-p
  92 Used by
  93 .BR getty (8)
  94 to tell
  95 .B login
  96 not to destroy the environment.
  97 .TP
  98 .B \-f
  99 Used to skip a second login authentication.  This specifically does
 100 .B not
 101 work for root, and does not appear to work well under Linux.
 102 .TP
 103 .B \-h
 104 Used by other servers (i.e.,
 105 .BR telnetd (8))
 106 to pass the name of the remote host to
 107 .B login
 108 so that it may be placed in utmp and wtmp.  Only the superuser may
 109 use this option.
 110 .IP
 111 Note that the
 112 .B \-h
 113 option has impact on the
 114 .B PAM service
 115 .BR name .
 116 The standard service name is
 117 .IR login ,
 118 with the
 119 .B \-h
 120 option the name is
 121 .IR remote .
 122 It is necessary to create proper PAM config files (e.g.
 123 .I /etc\:/pam.d\:/login
 124 and
 125 .IR /etc\:/pam.d\:/remote ).
 126 .TP
 127 .B \-H
 128 Used by other servers (i.e.,
 129 .BR telnetd (8))
 130 to tell
 131 .B login
 132 that printing the hostname should be suppressed in the login: prompt.
 133 See also LOGIN_PLAIN_PROMPT below if your server does not allow to configure
 134 .B login
 135 command line.
 136 .TP
 137 \fB\-\-help\fR
 138 Display help text and exit.
 139 .TP
 140 \fB\-V\fR, \fB\-\-version\fR
 141 Display version information and exit.
 142 .SH CONFIG FILE ITEMS
 143 .B login
 144 reads the
 145 .IR /etc\:/login.defs (5)
 146 configuration file.  Note that the configuration file could be
 147 distributed with another package (e.g. shadow-utils).  The following
 148 configuration items are relevant for
 149 .BR login (1):
 150 .PP
 151 .B MOTD_FILE
 152 (string)
 153 .RS 4
 154 If defined, a ":" delimited list of "message of the day" files to be
 155 displayed upon login.  The default value is
 156 .IR /etc\:/motd .
 157 If the
 158 .B MOTD_FILE
 159 item is empty or a quiet login is enabled, then the message of the day
 160 is not displayed.  Note that the same functionality is also provided
 161 by
 162 .BR pam_motd (8)
 163 PAM module.
 164 .RE
 165 .PP
 166 .B LOGIN_PLAIN_PROMPT
 167 (boolean)
 168 .RS 4
 169 Tell login that printing the hostname should be suppressed in the login:
 170 prompt.  This is alternative to the \fB\-H\fR command line option.  The default
 171 value is
 172 .IR no .
 173 .RE
 174 .PP
 175 .B LOGIN_TIMEOUT
 176 (number)
 177 .RS 4
 178 Max time in seconds for login.  The default value is
 179 .IR 60 .
 180 .RE
 181 .PP
 182 .B LOGIN_RETRIES
 183 (number)
 184 .RS 4
 185 Maximum number of login retries in case of a bad password.  The default
 186 value is
 187 .IR 3 .
 188 .RE
 189 .PP
 190 .B FAIL_DELAY
 191 (number)
 192 .RS 4
 193 Delay in seconds before being allowed another three tries after a
 194 login failure.  The default value is
 195 .IR 5 .
 196 .RE
 197 .PP
 198 .B TTYPERM
 199 (string)
 200 .RS 4
 201 The terminal permissions.  The default value is
 202 .I 0600
 203 or
 204 .I 0620
 205 if tty group is used.
 206 .RE
 207 .PP
 208 .B TTYGROUP
 209 (string)
 210 .RS 4
 211 The login tty will be owned by the
 212 .BR TTYGROUP .
 213 The default value is
 214 .IR tty .
 215 If the
 216 .B TTYGROUP
 217 does not exist, then the ownership of the terminal is set to the
 218 user\'s primary group.
 219 .PP
 220 The
 221 .B TTYGROUP
 222 can be either the name of a group or a numeric group identifier.
 223 .RE
 224 .PP
 225 .B HUSHLOGIN_FILE
 226 (string)
 227 .RS 4
 228 If defined, this file can inhibit all the usual chatter during the
 229 login sequence.  If a full pathname (e.g.
 230 .IR /etc\:/hushlogins )
 231 is specified, then hushed mode will be enabled if the user\'s name or
 232 shell are found in the file.  If this global hush login file is empty
 233 then the hushed mode will be enabled for all users.
 234 .PP
 235 If a full pathname is not specified, then hushed mode will be enabled
 236 if the file exists in the user\'s home directory.
 237 .PP
 238 The default is to check
 239 .I /etc\:/hushlogins
 240 and if it does not exist then
 241 .I ~/.hushlogin
 242 .PP
 243 If the
 244 .B HUSHLOGIN_FILE
 245 item is empty, then all the checks are disabled.
 246 .RE
 247 .PP
 248 .B DEFAULT_HOME
 249 (boolean)
 250 .RS 4
 251 Indicate if login is allowed if we cannot change directory to the
 252 home directory.  If set to
 253 .IR yes ,
 254 the user will login in the root (/) directory if it is not possible
 255 to change directory to her home.  The default value is
 256 .IR yes .
 257 .RE
 258 .PP
 259 .B LASTLOG_UID_MAX
 260 (unsigned number)
 261 .RS 4
 262 Highest user ID number for which the lastlog entries should be
 263 updated.  As higher user IDs are usually tracked by remote user
 264 identity and authentication services there is no need to create
 265 a huge sparse lastlog file for them.  No LASTLOG_UID_MAX option
 266 present in the configuration means that there is no user ID limit
 267 for writing lastlog entries.
 268 .RE
 269 .PP
 270 .B LOG_UNKFAIL_ENAB
 271 (boolean)
 272 .RS 4
 273 Enable display of unknown usernames when login failures are recorded.
 274 The default value is
 275 .IR no .
 276 .PP
 277 Note that logging unknown usernames may be a security issue if a
 278 user enters her password instead of her login name.
 279 .RE
 280 .PP
 281 .B ENV_PATH
 282 (string)
 283 .RS 4
 284 If set, it will be used to define the PATH environment variable when
 285 a regular user logs in.  The default value is
 286 .I /usr\:/local\:/bin:\:/bin:\:/usr\:/bin
 287 .RE
 288 .PP
 289 .B ENV_ROOTPATH
 290 (string)
 291 .br
 292 .B ENV_SUPATH
 293 (string)
 294 .RS 4
 295 If set, it will be used to define the PATH environment variable when
 296 the superuser logs in.  ENV_ROOTPATH takes precedence.  The default value is
 297 .I /usr\:/local\:/sbin:\:/usr\:/local\:/bin:\:/sbin:\:/bin:\:/usr\:/sbin:\:/usr\:/bin
 298 .RE
 299 .SH FILES
 300 .nf
 301 .I /var/run/utmp
 302 .I /var/log/wtmp
 303 .I /var/log/lastlog
 304 .I /var/spool/mail/*
 305 .I /etc/motd
 306 .I /etc/passwd
 307 .I /etc/nologin
 308 .I /etc/pam.d/login
 309 .I /etc/pam.d/remote
 310 .I /etc/hushlogins
 311 .I .hushlogin
 312 .fi
 313 .SH "SEE ALSO"
 314 .BR mail (1),
 315 .BR passwd (1),
 316 .BR passwd (5),
 317 .BR environ (7),
 318 .BR getty (8),
 319 .BR init (8),
 320 .BR shutdown (8)
 321 .SH BUGS
 322 The undocumented BSD
 323 .B \-r
 324 option is not supported.  This may be required by some
 325 .BR rlogind (8)
 326 programs.
 327 .PP
 328 A recursive login, as used to be possible in the good old days, no
 329 longer works; for most purposes
 330 .BR su (1)
 331 is a satisfactory substitute.  Indeed, for security reasons, login
 332 does a vhangup() system call to remove any possible listening
 333 processes on the tty.  This is to avoid password sniffing.  If one
 334 uses the command
 335 .BR login ,
 336 then the surrounding shell gets killed by vhangup() because it's no
 337 longer the true owner of the tty.  This can be avoided by using
 338 .B exec login
 339 in a top-level shell or xterm.
 340 .SH AUTHOR
 341 Derived from BSD login 5.40 (5/9/89) by
 342 .MT glad@\:daimi.\:dk
 343 Michael Glad
 344 .ME
 345 for HP-UX
 346 .br
 347 Ported to Linux 0.12:
 348 .MT poe@\:daimi.\:aau.\:dk
 349 Peter Orbaek
 350 .ME
 351 .br
 352 Rewritten to a PAM-only version by
 353 .MT kzak@\:redhat.\:com
 354 Karel Zak
 355 .ME
 356 .SH AVAILABILITY
 357 The login command is part of the util-linux package and is
 358 available from
 359 .UR https://\:www.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
 360 Linux Kernel Archive
 361 .UE .