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 .BR \-p
  10 ] [
  11 .BR \-h
  12 .IR host
  13 ] [
  14 .BR \-H
  15 ] [
  16 .BR \-f
  17 .IR username
  18 |
  19 .IR 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 .TP
 134 \fB\-\-help\fR
 135 Display help text and exit.
 136 .TP
 137 \fB\-V\fR, \fB\-\-version\fR
 138 Display version information and exit.
 139 .SH CONFIG FILE ITEMS
 140 .B login
 141 reads the
 142 .IR /etc\:/login.defs (5)
 143 configuration file.  Note that the configuration file could be
 144 distributed with another package (e.g. shadow-utils).  The following
 145 configuration items are relevant for
 146 .BR login (1):
 147 .PP
 148 .B MOTD_FILE
 149 (string)
 150 .RS 4
 151 If defined, a ":" delimited list of "message of the day" files to be
 152 displayed upon login.  The default value is
 153 .IR /etc\:/motd .
 154 If the
 155 .B MOTD_FILE
 156 item is empty or a quiet login is enabled, then the message of the day
 157 is not displayed.  Note that the same functionality is also provided
 158 by
 159 .BR pam_motd (8)
 160 PAM module.
 161 .RE
 162 .PP
 163 .B LOGIN_TIMEOUT
 164 (number)
 165 .RS 4
 166 Max time in seconds for login.  The default value is
 167 .IR 60 .
 168 .RE
 169 .PP
 170 .B LOGIN_RETRIES
 171 (number)
 172 .RS 4
 173 Maximum number of login retries in case of a bad password.  The default
 174 value is
 175 .IR 3 .
 176 .RE
 177 .PP
 178 .B FAIL_DELAY
 179 (number)
 180 .RS 4
 181 Delay in seconds before being allowed another three tries after a
 182 login failure.  The default value is
 183 .IR 5 .
 184 .RE
 185 .PP
 186 .B TTYPERM
 187 (string)
 188 .RS 4
 189 The terminal permissions.  The default value is
 190 .IR 0600
 191 or
 192 .IR 0620
 193 if tty group is used.
 194 .RE
 195 .PP
 196 .B TTYGROUP
 197 (string)
 198 .RS 4
 199 The login tty will be owned by the
 200 .BR TTYGROUP .
 201 The default value is
 202 .IR tty .
 203 If the
 204 .B TTYGROUP
 205 does not exist, then the ownership of the terminal is set to the
 206 user\'s primary group.
 207 .PP
 208 The
 209 .B TTYGROUP
 210 can be either the name of a group or a numeric group identifier.
 211 .RE
 212 .PP
 213 .B HUSHLOGIN_FILE
 214 (string)
 215 .RS 4
 216 If defined, this file can inhibit all the usual chatter during the
 217 login sequence.  If a full pathname (e.g.
 218 .IR /etc\:/hushlogins )
 219 is specified, then hushed mode will be enabled if the user\'s name or
 220 shell are found in the file.  If this global hush login file is empty
 221 then the hushed mode will be enabled for all users.
 222 .PP
 223 If a full pathname is not specified, then hushed mode will be enabled
 224 if the file exists in the user\'s home directory.
 225 .PP
 226 The default is to check
 227 .I /etc\:/hushlogins
 228 and if it does not exist then
 229 .I ~/.hushlogin
 230 .PP
 231 If the
 232 .B HUSHLOGIN_FILE
 233 item is empty, then all the checks are disabled.
 234 .RE
 235 .PP
 236 .B DEFAULT_HOME
 237 (boolean)
 238 .RS 4
 239 Indicate if login is allowed if we cannot change directory to the
 240 home directory.  If set to
 241 .IR yes ,
 242 the user will login in the root (/) directory if it is not possible
 243 to change directory to her home.  The default value is
 244 .IR yes .
 245 .RE
 246 .PP
 247 .B LOG_UNKFAIL_ENAB
 248 (boolean)
 249 .RS 4
 250 Enable display of unknown usernames when login failures are recorded.
 251 The default value is
 252 .IR no .
 253 .PP
 254 Note that logging unknown usernames may be a security issue if a
 255 user enters her password instead of her login name.
 256 .RE
 257 .PP
 258 .B ENV_PATH
 259 (string)
 260 .RS 4
 261 If set, it will be used to define the PATH environment variable when
 262 a regular user logs in.  The default value is
 263 .I /usr\:/local\:/bin:\:/bin:\:/usr\:/bin
 264 .RE
 265 .PP
 266 .B ENV_ROOTPATH
 267 (string)
 268 .br
 269 .B ENV_SUPATH
 270 (string)
 271 .RS 4
 272 If set, it will be used to define the PATH environment variable when
 273 the superuser logs in.  The default value is
 274 .I /usr\:/local\:/sbin:\:/usr\:/local\:/bin:\:/sbin:\:/bin:\:/usr\:/sbin:\:/usr\:/bin
 275 .RE
 276 .SH FILES
 277 .nf
 278 .I /var/run/utmp
 279 .I /var/log/wtmp
 280 .I /var/log/lastlog
 281 .I /var/spool/mail/*
 282 .I /etc/motd
 283 .I /etc/passwd
 284 .I /etc/nologin
 285 .I /etc/pam.d/login
 286 .I /etc/pam.d/remote
 287 .I /etc/hushlogins
 288 .I .hushlogin
 289 .fi
 290 .SH "SEE ALSO"
 291 .BR mail (1),
 292 .BR passwd (1),
 293 .BR passwd (5),
 294 .BR environ (7),
 295 .BR getty (8),
 296 .BR init (8),
 297 .BR shutdown (8)
 298 .SH BUGS
 299 The undocumented BSD
 300 .B \-r
 301 option is not supported.  This may be required by some
 302 .BR rlogind (8)
 303 programs.
 304 .PP
 305 A recursive login, as used to be possible in the good old days, no
 306 longer works; for most purposes
 307 .BR su (1)
 308 is a satisfactory substitute.  Indeed, for security reasons, login
 309 does a vhangup() system call to remove any possible listening
 310 processes on the tty.  This is to avoid password sniffing.  If one
 311 uses the command
 312 .BR login ,
 313 then the surrounding shell gets killed by vhangup() because it's no
 314 longer the true owner of the tty.  This can be avoided by using
 315 .B exec login
 316 in a top-level shell or xterm.
 317 .SH AUTHOR
 318 Derived from BSD login 5.40 (5/9/89) by
 319 .MT glad@\:daimi.\:dk
 320 Michael Glad
 321 .ME
 322 for HP-UX
 323 .br
 324 Ported to Linux 0.12:
 325 .MT poe@\:daimi.\:aau.\:dk
 326 Peter Orbaek
 327 .ME
 328 .br
 329 Rewritten to a PAM-only version by
 330 .MT kzak@\:redhat.\:com
 331 Karel Zak
 332 .ME
 333 .SH AVAILABILITY
 334 The login command is part of the util-linux package and is
 335 available from
 336 .UR https://\:www.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
 337 Linux Kernel Archive
 338 .UE .