1AGETTY(8) System Administration AGETTY(8)
2
6 agetty - alternative Linux getty
7
10 agetty [options] port [baud_rate...] [term]
11
14 agetty opens a tty port, prompts for a login name and invokes the
15 /bin/login command. It is normally invoked by init(8).
16 agetty has several non-standard features that are useful for hardwired
18 and for dial-in lines:
19 · Adapts the tty settings to parity bits and to erase, kill, end-
21 of-line and uppercase characters when it reads a login name.
22 The program can handle 7-bit characters with even, odd, none or
23 space parity, and 8-bit characters with no parity. The follow‐
24 ing special characters are recognized: Control-U (kill); DEL and
25 backspace (erase); carriage return and line feed (end of line).
26 See also the --erase-chars and --kill-chars options.
27 · Optionally deduces the baud rate from the CONNECT messages pro‐
29 duced by Hayes(tm)-compatible modems.
30 · Optionally does not hang up when it is given an already opened
32 line (useful for call-back applications).
33 · Optionally does not display the contents of the /etc/issue file.
35 · Optionally displays an alternative issue file or directory
37 instead of /etc/issue or /etc/issue.d.
38 · Optionally does not ask for a login name.
40 · Optionally invokes a non-standard login program instead of
42 /bin/login.
43 · Optionally turns on hardware flow control.
45 · Optionally forces the line to be local with no need for carrier
47 detect.
48 This program does not use the /etc/gettydefs (System V) or /etc/get‐
50 tytab (SunOS 4) files.
51
53 port A path name relative to the /dev directory. If a "-" is speci‐
54 fied, agetty assumes that its standard input is already con‐
55 nected to a tty port and that a connection to a remote user has
56 already been established.
57 Under System V, a "-" port argument should be preceded by a
59 "--".
60 baud_rate,...
62 A comma-separated list of one or more baud rates. Each time
63 agetty receives a BREAK character it advances through the list,
64 which is treated as if it were circular.
65 Baud rates should be specified in descending order, so that the
67 null character (Ctrl-@) can also be used for baud-rate switch‐
68 ing.
69 This argument is optional and unnecessary for virtual terminals.
71 The default for serial terminals is keep the current baud rate
73 (see --keep-baud) and if unsuccessful then default to '9600'.
74 term The value to be used for the TERM environment variable. This
76 overrides whatever init(8) may have set, and is inherited by
77 login and the shell.
78 The default is 'vt100', or 'linux' for Linux on a virtual termi‐
80 nal, or 'hurd' for GNU Hurd on a virtual terminal.
81
83 -8, --8bits
84 Assume that the tty is 8-bit clean, hence disable parity detec‐
85 tion.
86 -a, --autologin username
88 Automatically log in the specified user without asking for a
89 username or password. Using this option causes an -f username
90 option and argument to be added to the /bin/login command line.
91 See --login-options, which can be used to modify this option's
92 behavior.
93 Note that --autologin may affect the way how agetty initializes
95 the serial line, because on auto-login agetty does not read from
96 the line and it has no opportunity optimize the line setting.
97 -c, --noreset
99 Do not reset terminal cflags (control modes). See termios(3)
100 for more details.
101 -E, --remote
103 Typically the login(1) command is given a remote hostname when
104 called by something such as telnetd(8). This option allows
105 agetty to pass what it is using for a hostname to login(1) for
106 use in utmp(5). See --host, login(1), and utmp(5).
107 If the --host fakehost option is given, then an -h fakehost
109 option and argument are added to the /bin/login command line.
110 If the --nohostname option is given, then an -H option is added
112 to the /bin/login command line.
113 See --login-options.
115 -f, --issue-file file|directory
117 Display the contents of file instead of /etc/issue. If the
118 specified path is a directory then displays all files with
119 .issue file extension in version-sort order from the directory.
120 This allows custom messages to be displayed on different termi‐
121 nals. The --noissue option will override this option.
122 -h, --flow-control
124 Enable hardware (RTS/CTS) flow control. It is left up to the
125 application to disable software (XON/XOFF) flow protocol where
126 appropriate.
127 -H, --host fakehost
129 Write the specified fakehost into the utmp file. Normally, no
130 login host is given, since agetty is used for local hardwired
131 connections and consoles. However, this option can be useful
132 for identifying terminal concentrators and the like.
133 -i, --noissue
135 Do not display the contents of /etc/issue (or other) before
136 writing the login prompt. Terminals or communications hardware
137 may become confused when receiving lots of text at the wrong
138 baud rate; dial-up scripts may fail if the login prompt is pre‐
139 ceded by too much text.
140 -I, --init-string initstring
142 Set an initial string to be sent to the tty or modem before
143 sending anything else. This may be used to initialize a modem.
144 Non-printable characters may be sent by writing their octal code
145 preceded by a backslash (\). For example, to send a linefeed
146 character (ASCII 10, octal 012), write \012.
147 -J, --noclear
149 Do not clear the screen before prompting for the login name. By
150 default the screen is cleared.
151 -l, --login-program login_program
153 Invoke the specified login_program instead of /bin/login. This
154 allows the use of a non-standard login program. Such a program
155 could, for example, ask for a dial-up password or use a differ‐
156 ent password file. See --login-options.
157 -L, --local-line[=mode]
159 Control the CLOCAL line flag. The optional mode argument is
160 'auto', 'always' or 'never'. If the mode argument is omitted,
161 then the default is 'always'. If the --local-line option is not
162 given at all, then the default is 'auto'.
163 always Forces the line to be a local line with no need for car‐
165 rier detect. This can be useful when you have a locally
166 attached terminal where the serial line does not set the
167 carrier-detect signal.
168 never Explicitly clears the CLOCAL flag from the line setting
170 and the carrier-detect signal is expected on the line.
171 auto The agetty default. Does not modify the CLOCAL setting
173 and follows the setting enabled by the kernel.
174 -m, --extract-baud
176 Try to extract the baud rate from the CONNECT status message
177 produced by Hayes(tm)-compatible modems. These status messages
178 are of the form: "<junk><speed><junk>". agetty assumes that the
179 modem emits its status message at the same speed as specified
180 with (the first) baud_rate value on the command line.
181 Since the --extract-baud feature may fail on heavily-loaded sys‐
183 tems, you still should enable BREAK processing by enumerating
184 all expected baud rates on the command line.
185 --list-speeds
187 Display supported baud rates. These are determined at compila‐
188 tion time.
189 -n, --skip-login
191 Do not prompt the user for a login name. This can be used in
192 connection with the --login-program option to invoke a non-stan‐
193 dard login process such as a BBS system. Note that with the
194 --skip-login option, agetty gets no input from the user who logs
195 in and therefore will not be able to figure out parity, charac‐
196 ter size, and newline processing of the connection. It defaults
197 to space parity, 7 bit characters, and ASCII CR (13) end-of-line
198 character. Beware that the program that agetty starts (usually
199 /bin/login) is run as root.
200 -N, --nonewline
202 Do not print a newline before writing out /etc/issue.
203 -o, --login-options "login_options"
205 Options and arguments that are passed to login(1). Where \u is
206 replaced by the login name. For example:
207 --login-options '-h darkstar -- \u'
209 See --autologin, --login-program and --remote.
211 Please read the SECURITY NOTICE below before using this option.
213 -p, --login-pause
215 Wait for any key before dropping to the login prompt. Can be
216 combined with --autologin to save memory by lazily spawning
217 shells.
218 -r, --chroot directory
220 Change root to the specified directory.
221 -R, --hangup
223 Call vhangup() to do a virtual hangup of the specified terminal.
224 -s, --keep-baud
226 Try to keep the existing baud rate. The baud rates from the
227 command line are used when agetty receives a BREAK character.
228 -t, --timeout timeout
230 Terminate if no user name could be read within timeout seconds.
231 Use of this option with hardwired terminal lines is not recom‐
232 mended.
233 -U, --detect-case
235 Turn on support for detecting an uppercase-only terminal. This
236 setting will detect a login name containing only capitals as
237 indicating an uppercase-only terminal and turn on some upper-to-
238 lower case conversions. Note that this has no support for any
239 Unicode characters.
240 -w, --wait-cr
242 Wait for the user or the modem to send a carriage-return or a
243 linefeed character before sending the /etc/issue file (or oth‐
244 ers) and the login prompt. This is useful with the
245 --init-string option.
246 --nohints
248 Do not print hints about Num, Caps and Scroll Locks.
249 --nohostname
251 By default the hostname will be printed. With this option
252 enabled, no hostname at all will be shown.
253 --long-hostname
255 By default the hostname is only printed until the first dot.
256 With this option enabled, the fully qualified hostname by geth‐
257 ostname(3P) or (if not found) by getaddrinfo(3) is shown.
258 --erase-chars string
260 This option specifies additional characters that should be
261 interpreted as a backspace ("ignore the previous character")
262 when the user types the login name. The default additional
263 ´erase´ has been ´#´, but since util-linux 2.23 no additional
264 erase characters are enabled by default.
265 --kill-chars string
267 This option specifies additional characters that should be
268 interpreted as a kill ("ignore all previous characters") when
269 the user types the login name. The default additional ´kill´
270 has been ´@´, but since util-linux 2.23 no additional kill char‐
271 acters are enabled by default.
272 --chdir directory
274 Change directory before the login.
275 --delay number
277 Sleep seconds before open tty.
278 --nice number
280 Run login with this priority.
281 --reload
283 Ask all running agetty instances to reload and update their dis‐
284 played prompts, if the user has not yet commenced logging in.
285 After doing so the command will exit. This feature might be
286 unsupported on systems without Linux inotify(7).
287 --version
289 Display version information and exit.
290 --help Display help text and exit.
292
294 This section shows examples for the process field of an entry in the
295 /etc/inittab file. You'll have to prepend appropriate values for the
296 other fields. See inittab(5) for more details.
297 For a hardwired line or a console tty:
299 /sbin/agetty 9600 ttyS1
301 For a directly connected terminal without proper carrier-detect wiring
303 (try this if your terminal just sleeps instead of giving you a pass‐
304 word: prompt):
305 /sbin/agetty --local-line 9600 ttyS1 vt100
307 For an old-style dial-in line with a 9600/2400/1200 baud modem:
309 /sbin/agetty --extract-baud --timeout 60 ttyS1 9600,2400,1200
311 For a Hayes modem with a fixed 115200 bps interface to the machine (the
313 example init string turns off modem echo and result codes, makes
314 modem/computer DCD track modem/modem DCD, makes a DTR drop cause a dis‐
315 connection, and turns on auto-answer after 1 ring):
316 /sbin/agetty --wait-cr --init-string 'ATE0Q1&D2&C1S0=1 15' 115200 ttyS1
318
321 If you use the --login-program and --login-options options, be aware
322 that a malicious user may try to enter lognames with embedded options,
323 which then get passed to the used login program. Agetty does check for
324 a leading "-" and makes sure the logname gets passed as one parameter
325 (so embedded spaces will not create yet another parameter), but depend‐
326 ing on how the login binary parses the command line that might not be
327 sufficient. Check that the used login program cannot be abused this
328 way.
329 Some programs use "--" to indicate that the rest of the commandline
331 should not be interpreted as options. Use this feature if available by
332 passing "--" before the username gets passed by \u.
333
336 The default issue file is /etc/issue. If the file exists then agetty
337 also checks for /etc/issue.d directory. The directory is optional
338 extension to the default issue file and content of the directory is
339 printed after /etc/issue content. If the /etc/issue does not exist than
340 the directory is ignored. All files with .issue extension from the
341 directory are printed in version-sort order. The directory allow to
342 maintain 3rd-party messages independently on the primary system
343 /etc/issue file.
344 The default path maybe overridden by --issue-file option. In this case
346 specified path has to be file or directory and the default /etc/issue
347 as well as /etc/issue.d are ignored.
348 The issue files may contain certain escape codes to display the system
350 name, date, time etcetera. All escape codes consist of a backslash (\)
351 immediately followed by one of the characters listed below.
352 4 or 4{interface}
355 Insert the IPv4 address of the specified network interface (for
356 example: \4{eth0}). If the interface argument is not specified,
357 then select the first fully configured (UP, non-LOCALBACK, RUN‐
358 NING) interface. If not any configured interface is found, fall
359 back to the IP address of the machine's hostname.
360 6 or 6{interface}
362 The same as \4 but for IPv6.
363 b Insert the baudrate of the current line.
365 d Insert the current date.
367 e or e{name}
369 Translate the human-readable name to an escape sequence and
370 insert it (for example: \e{red}Alert text.\e{reset}). If the
371 name argument is not specified, then insert \033. The currently
372 supported names are: black, blink, blue, bold, brown, cyan,
373 darkgray, gray, green, halfbright, lightblue, lightcyan,
374 lightgray, lightgreen, lightmagenta, lightred, magenta, red,
375 reset, reverse, and yellow. All unknown names are silently
376 ignored.
377 s Insert the system name (the name of the operating system). Same
379 as 'uname -s'. See also the \S escape code.
380 S or S{VARIABLE}
382 Insert the VARIABLE data from /etc/os-release. If this file
383 does not exist then fall back to /usr/lib/os-release. If the
384 VARIABLE argument is not specified, then use PRETTY_NAME from
385 the file or the system name (see \s). This escape code allows
386 to keep /etc/issue distribution and release independent. Note
387 that \S{ANSI_COLOR} is converted to the real terminal escape
388 sequence.
389 l Insert the name of the current tty line.
391 m Insert the architecture identifier of the machine. Same as
393 'uname -m'.
394 n Insert the nodename of the machine, also known as the hostname.
396 Same as 'uname -n'.
397 o Insert the NIS domainname of the machine. Same as 'hostname
399 -d'.
400 O Insert the DNS domainname of the machine.
402 r Insert the release number of the OS. Same as 'uname -r'.
404 t Insert the current time.
406 u Insert the number of current users logged in.
408 U Insert the string "1 user" or "<n> users" where <n> is the num‐
410 ber of current users logged in.
411 v Insert the version of the OS, that is, the build-date and such.
413 An example. On my system, the following /etc/issue file:
415 This is \n.\o (\s \m \r) \t
417 displays as:
419 This is thingol.orcan.dk (Linux i386 1.1.9) 18:29:30
421
424 /var/run/utmp
425 the system status file.
426 /etc/issue
428 printed before the login prompt.
429 /etc/os-release /usr/lib/os-release
431 operating system identification data.
432 /dev/console
434 problem reports (if syslog(3) is not used).
435 /etc/inittab
437 init(8) configuration file for SysV-style init daemon.
438
440 The baud-rate detection feature (the --extract-baud option) requires
441 that agetty be scheduled soon enough after completion of a dial-in call
442 (within 30 ms with modems that talk at 2400 baud). For robustness,
443 always use the --extract-baud option in combination with a multiple
444 baud rate command-line argument, so that BREAK processing is enabled.
445 The text in the /etc/issue file (or other) and the login prompt are
447 always output with 7-bit characters and space parity.
448 The baud-rate detection feature (the --extract-baud option) requires
450 that the modem emits its status message after raising the DCD line.
451
453 Depending on how the program was configured, all diagnostics are writ‐
454 ten to the console device or reported via the syslog(3) facility.
455 Error messages are produced if the port argument does not specify a
456 terminal device; if there is no utmp entry for the current process
457 (System V only); and so on.
458
460 Werner Fink ⟨werner@suse.de⟩
461 Karel Zak ⟨kzak@redhat.com⟩
462 The original agetty for serial terminals was written by W.Z. Venema
464 <wietse@wzv.win.tue.nl> and ported to Linux by Peter Orbaek
465 <poe@daimi.aau.dk>.
466
469 The agetty command is part of the util-linux package and is available
470 from https://www.kernel.org/pub/linux/utils/util-linux/.
471util-linux February 2016 AGETTY(8)