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