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 (or other).
118 If the specified path is a directory then displays all files
119 with .issue file extension in version-sort order from the direc‐
120 tory. This allows custom messages to be displayed on different
121 terminals. The --noissue option will override this option.
122 --show-issue
124 Display the current issue file (or other) on the current termi‐
125 nal and exit. Use this option to review the current setting, it
126 is not designed for any other purpose. Note that output may use
127 some default or incomplete information as proper output depends
128 on terminal and agetty command line.
129 -h, --flow-control
131 Enable hardware (RTS/CTS) flow control. It is left up to the
132 application to disable software (XON/XOFF) flow protocol where
133 appropriate.
134 -H, --host fakehost
136 Write the specified fakehost into the utmp file. Normally, no
137 login host is given, since agetty is used for local hardwired
138 connections and consoles. However, this option can be useful
139 for identifying terminal concentrators and the like.
140 -i, --noissue
142 Do not display the contents of /etc/issue (or other) before
143 writing the login prompt. Terminals or communications hardware
144 may become confused when receiving lots of text at the wrong
145 baud rate; dial-up scripts may fail if the login prompt is pre‐
146 ceded by too much text.
147 -I, --init-string initstring
149 Set an initial string to be sent to the tty or modem before
150 sending anything else. This may be used to initialize a modem.
151 Non-printable characters may be sent by writing their octal code
152 preceded by a backslash (\). For example, to send a linefeed
153 character (ASCII 10, octal 012), write \012.
154 -J, --noclear
156 Do not clear the screen before prompting for the login name. By
157 default the screen is cleared.
158 -l, --login-program login_program
160 Invoke the specified login_program instead of /bin/login. This
161 allows the use of a non-standard login program. Such a program
162 could, for example, ask for a dial-up password or use a differ‐
163 ent password file. See --login-options.
164 -L, --local-line[=mode]
166 Control the CLOCAL line flag. The optional mode argument is
167 'auto', 'always' or 'never'. If the mode argument is omitted,
168 then the default is 'always'. If the --local-line option is not
169 given at all, then the default is 'auto'.
170 always Forces the line to be a local line with no need for car‐
172 rier detect. This can be useful when you have a locally
173 attached terminal where the serial line does not set the
174 carrier-detect signal.
175 never Explicitly clears the CLOCAL flag from the line setting
177 and the carrier-detect signal is expected on the line.
178 auto The agetty default. Does not modify the CLOCAL setting
180 and follows the setting enabled by the kernel.
181 -m, --extract-baud
183 Try to extract the baud rate from the CONNECT status message
184 produced by Hayes(tm)-compatible modems. These status messages
185 are of the form: "<junk><speed><junk>". agetty assumes that the
186 modem emits its status message at the same speed as specified
187 with (the first) baud_rate value on the command line.
188 Since the --extract-baud feature may fail on heavily-loaded sys‐
190 tems, you still should enable BREAK processing by enumerating
191 all expected baud rates on the command line.
192 --list-speeds
194 Display supported baud rates. These are determined at compila‐
195 tion time.
196 -n, --skip-login
198 Do not prompt the user for a login name. This can be used in
199 connection with the --login-program option to invoke a non-stan‐
200 dard login process such as a BBS system. Note that with the
201 --skip-login option, agetty gets no input from the user who logs
202 in and therefore will not be able to figure out parity, charac‐
203 ter size, and newline processing of the connection. It defaults
204 to space parity, 7 bit characters, and ASCII CR (13) end-of-line
205 character. Beware that the program that agetty starts (usually
206 /bin/login) is run as root.
207 -N, --nonewline
209 Do not print a newline before writing out /etc/issue.
210 -o, --login-options "login_options"
212 Options and arguments that are passed to login(1). Where \u is
213 replaced by the login name. For example:
214 --login-options '-h darkstar -- \u'
216 See --autologin, --login-program and --remote.
218 Please read the SECURITY NOTICE below before using this option.
220 -p, --login-pause
222 Wait for any key before dropping to the login prompt. Can be
223 combined with --autologin to save memory by lazily spawning
224 shells.
225 -r, --chroot directory
227 Change root to the specified directory.
228 -R, --hangup
230 Call vhangup() to do a virtual hangup of the specified terminal.
231 -s, --keep-baud
233 Try to keep the existing baud rate. The baud rates from the
234 command line are used when agetty receives a BREAK character.
235 -t, --timeout timeout
237 Terminate if no user name could be read within timeout seconds.
238 Use of this option with hardwired terminal lines is not recom‐
239 mended.
240 -U, --detect-case
242 Turn on support for detecting an uppercase-only terminal. This
243 setting will detect a login name containing only capitals as
244 indicating an uppercase-only terminal and turn on some upper-to-
245 lower case conversions. Note that this has no support for any
246 Unicode characters.
247 -w, --wait-cr
249 Wait for the user or the modem to send a carriage-return or a
250 linefeed character before sending the /etc/issue file (or oth‐
251 ers) and the login prompt. This is useful with the
252 --init-string option.
253 --nohints
255 Do not print hints about Num, Caps and Scroll Locks.
256 --nohostname
258 By default the hostname will be printed. With this option
259 enabled, no hostname at all will be shown.
260 --long-hostname
262 By default the hostname is only printed until the first dot.
263 With this option enabled, the fully qualified hostname by geth‐
264 ostname(3P) or (if not found) by getaddrinfo(3) is shown.
265 --erase-chars string
267 This option specifies additional characters that should be
268 interpreted as a backspace ("ignore the previous character")
269 when the user types the login name. The default additional
270 ´erase´ has been ´#´, but since util-linux 2.23 no additional
271 erase characters are enabled by default.
272 --kill-chars string
274 This option specifies additional characters that should be
275 interpreted as a kill ("ignore all previous characters") when
276 the user types the login name. The default additional ´kill´
277 has been ´@´, but since util-linux 2.23 no additional kill char‐
278 acters are enabled by default.
279 --chdir directory
281 Change directory before the login.
282 --delay number
284 Sleep seconds before open tty.
285 --nice number
287 Run login with this priority.
288 --reload
290 Ask all running agetty instances to reload and update their dis‐
291 played prompts, if the user has not yet commenced logging in.
292 After doing so the command will exit. This feature might be
293 unsupported on systems without Linux inotify(7).
294 --version
296 Display version information and exit.
297 --help Display help text and exit.
299
301 This section shows examples for the process field of an entry in the
302 /etc/inittab file. You'll have to prepend appropriate values for the
303 other fields. See inittab(5) for more details.
304 For a hardwired line or a console tty:
306 /sbin/agetty 9600 ttyS1
308 For a directly connected terminal without proper carrier-detect wiring
310 (try this if your terminal just sleeps instead of giving you a pass‐
311 word: prompt):
312 /sbin/agetty --local-line 9600 ttyS1 vt100
314 For an old-style dial-in line with a 9600/2400/1200 baud modem:
316 /sbin/agetty --extract-baud --timeout 60 ttyS1 9600,2400,1200
318 For a Hayes modem with a fixed 115200 bps interface to the machine (the
320 example init string turns off modem echo and result codes, makes
321 modem/computer DCD track modem/modem DCD, makes a DTR drop cause a dis‐
322 connection, and turns on auto-answer after 1 ring):
323 /sbin/agetty --wait-cr --init-string 'ATE0Q1&D2&C1S0=1 15' 115200 ttyS1
325
328 If you use the --login-program and --login-options options, be aware
329 that a malicious user may try to enter lognames with embedded options,
330 which then get passed to the used login program. Agetty does check for
331 a leading "-" and makes sure the logname gets passed as one parameter
332 (so embedded spaces will not create yet another parameter), but depend‐
333 ing on how the login binary parses the command line that might not be
334 sufficient. Check that the used login program cannot be abused this
335 way.
336 Some programs use "--" to indicate that the rest of the command line
338 should not be interpreted as options. Use this feature if available by
339 passing "--" before the username gets passed by \u.
340
343 The default issue file is /etc/issue. If the file exists then agetty
344 also checks for /etc/issue.d directory. The directory is optional
345 extension to the default issue file and content of the directory is
346 printed after /etc/issue content. If the /etc/issue does not exist than
347 the directory is ignored. All files with .issue extension from the
348 directory are printed in version-sort order. The directory allow to
349 maintain 3rd-party messages independently on the primary system
350 /etc/issue file.
351 Since version 2.35 additional locations for issue file and directory
353 are supported. If the default /etc/issue does not exist than agetty
354 checks for /run/issue and /run/issue.d, thereafter for /usr/lib/issue
355 and /usr/lib/issue.d. The directory /etc is expected for host specific
356 configuration, /run is expected for generated stuff and /usr/lib for
357 static distribution maintained configuration.
358 The default path maybe overridden by --issue-file option. In this case
360 specified path has to be file or directory and all the default issue
361 file and directory locations are ignored.
362 The issue file feature is possible to completely disable by --noissue
364 option.
365 It is possible to review the current issue file by agetty --show-issue
367 on the current terminal.
368 The issue files may contain certain escape codes to display the system
370 name, date, time etcetera. All escape codes consist of a backslash (\)
371 immediately followed by one of the characters listed below.
372 4 or 4{interface}
375 Insert the IPv4 address of the specified network interface (for
376 example: \4{eth0}). If the interface argument is not specified,
377 then select the first fully configured (UP, non-LOCALBACK, RUN‐
378 NING) interface. If not any configured interface is found, fall
379 back to the IP address of the machine's hostname.
380 6 or 6{interface}
382 The same as \4 but for IPv6.
383 b Insert the baudrate of the current line.
385 d Insert the current date.
387 e or e{name}
389 Translate the human-readable name to an escape sequence and
390 insert it (for example: \e{red}Alert text.\e{reset}). If the
391 name argument is not specified, then insert \033. The currently
392 supported names are: black, blink, blue, bold, brown, cyan,
393 darkgray, gray, green, halfbright, lightblue, lightcyan,
394 lightgray, lightgreen, lightmagenta, lightred, magenta, red,
395 reset, reverse, and yellow. All unknown names are silently
396 ignored.
397 s Insert the system name (the name of the operating system). Same
399 as 'uname -s'. See also the \S escape code.
400 S or S{VARIABLE}
402 Insert the VARIABLE data from /etc/os-release. If this file
403 does not exist then fall back to /usr/lib/os-release. If the
404 VARIABLE argument is not specified, then use PRETTY_NAME from
405 the file or the system name (see \s). This escape code allows
406 to keep /etc/issue distribution and release independent. Note
407 that \S{ANSI_COLOR} is converted to the real terminal escape
408 sequence.
409 l Insert the name of the current tty line.
411 m Insert the architecture identifier of the machine. Same as
413 'uname -m'.
414 n Insert the nodename of the machine, also known as the hostname.
416 Same as 'uname -n'.
417 o Insert the NIS domainname of the machine. Same as 'hostname
419 -d'.
420 O Insert the DNS domainname of the machine.
422 r Insert the release number of the OS. Same as 'uname -r'.
424 t Insert the current time.
426 u Insert the number of current users logged in.
428 U Insert the string "1 user" or "<n> users" where <n> is the num‐
430 ber of current users logged in.
431 v Insert the version of the OS, that is, the build-date and such.
433 An example. On my system, the following /etc/issue file:
435 This is \n.\o (\s \m \r) \t
437 displays as:
439 This is thingol.orcan.dk (Linux i386 1.1.9) 18:29:30
441
444 /var/run/utmp
445 the system status file.
446 /etc/issue
448 printed before the login prompt.
449 /etc/os-release /usr/lib/os-release
451 operating system identification data.
452 /dev/console
454 problem reports (if syslog(3) is not used).
455 /etc/inittab
457 init(8) configuration file for SysV-style init daemon.
458
460 The baud-rate detection feature (the --extract-baud option) requires
461 that agetty be scheduled soon enough after completion of a dial-in call
462 (within 30 ms with modems that talk at 2400 baud). For robustness,
463 always use the --extract-baud option in combination with a multiple
464 baud rate command-line argument, so that BREAK processing is enabled.
465 The text in the /etc/issue file (or other) and the login prompt are
467 always output with 7-bit characters and space parity.
468 The baud-rate detection feature (the --extract-baud option) requires
470 that the modem emits its status message after raising the DCD line.
471
473 Depending on how the program was configured, all diagnostics are writ‐
474 ten to the console device or reported via the syslog(3) facility.
475 Error messages are produced if the port argument does not specify a
476 terminal device; if there is no utmp entry for the current process
477 (System V only); and so on.
478
480 Werner Fink ⟨werner@suse.de⟩
481 Karel Zak ⟨kzak@redhat.com⟩
482 The original agetty for serial terminals was written by W.Z. Venema
484 <wietse@wzv.win.tue.nl> and ported to Linux by Peter Orbaek
485 <poe@daimi.aau.dk>.
486
489 The agetty command is part of the util-linux package and is available
490 from https://www.kernel.org/pub/linux/utils/util-linux/.
491util-linux February 2016 AGETTY(8)