1AGETTY(8) System Manager's Manual AGETTY(8)
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6 agetty - alternative Linux getty
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10 agetty [-8ihLmnsUw] [-f issue_file] [-l login_program] [-I init] [-t
11 timeout] [-H login_host] port baud_rate,... [term]
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15 agetty opens a tty port, prompts for a login name and invokes the
16 /bin/login command. It is normally invoked by init(8).
17 agetty has several non-standard features that are useful for hard-wired
19 and for dial-in lines:
20 o Adapts the tty settings to parity bits and to erase, kill, end-
22 of-line and uppercase characters when it reads a login name.
23 The program can handle 7-bit characters with even, odd, none or
24 space parity, and 8-bit characters with no parity. The following
25 special characters are recognized: @ and Control-U (kill); #,
26 DEL and back space (erase); carriage return and line feed (end
27 of line).
28 o Optionally deduces the baud rate from the CONNECT messages pro‐
30 duced by Hayes(tm)-compatible modems.
31 o Optionally does not hang up when it is given an already opened
33 line (useful for call-back applications).
34 o Optionally does not display the contents of the /etc/issue file.
36 o Optionally displays an alternative issue file instead of
38 /etc/issue.
39 o Optionally does not ask for a login name.
41 o Optionally invokes a non-standard login program instead of
43 /bin/login.
44 o Optionally turns on hard-ware flow control
46 o Optionally forces the line to be local with no need for carrier
48 detect.
49 This program does not use the /etc/gettydefs (System V) or /etc/get‐
51 tytab (SunOS 4) files.
52
54 port A path name relative to the /dev directory. If a "-" is speci‐
55 fied, agetty assumes that its standard input is already con‐
56 nected to a tty port and that a connection to a remote user has
57 already been established.
58 Under System V, a "-" port argument should be preceded by a
60 "--".
61 baud_rate,...
63 A comma-separated list of one or more baud rates. Each time
64 agetty receives a BREAK character it advances through the list,
65 which is treated as if it were circular.
66 Baud rates should be specified in descending order, so that the
68 null character (Ctrl-@) can also be used for baud rate switch‐
69 ing.
70 term The value to be used for the TERM environment variable. This
72 overrides whatever init(8) may have set, and is inherited by
73 login and the shell.
74
76 -8 Assume that the tty is 8-bit clean, hence disable parity detec‐
77 tion.
78 -h Enable hardware (RTS/CTS) flow control. It is left up to the
80 application to disable software (XON/XOFF) flow protocol where
81 appropriate.
82 -i Do not display the contents of /etc/issue (or other) before
84 writing the login prompt. Terminals or communications hardware
85 may become confused when receiving lots of text at the wrong
86 baud rate; dial-up scripts may fail if the login prompt is pre‐
87 ceded by too much text.
88 -f issue_file
90 Display the contents of issue_file instead of /etc/issue. This
91 allows custom messages to be displayed on different terminals.
92 The -i option will override this option.
93 -I initstring
95 Set an initial string to be sent to the tty or modem before
96 sending anything else. This may be used to initialize a modem.
97 Non printable characters may be sent by writing their octal code
98 preceded by a backslash (\). For example to send a linefeed
99 character (ASCII 10, octal 012) write \012.
100 -l login_program
102 Invoke the specified login_program instead of /bin/login. This
103 allows the use of a non-standard login program (for example, one
104 that asks for a dial-up password or that uses a different pass‐
105 word file).
106 -H login_host
108 Write the specified login_host into the utmp file. (Normally, no
109 login host is given, since agetty is used for local hardwired
110 connections and consoles. However, this option can be useful for
111 identifying terminal concentrators and the like.
112 -m Try to extract the baud rate the CONNECT status message produced
114 by Hayes(tm)-compatible modems. These status messages are of the
115 form: "<junk><speed><junk>". agetty assumes that the modem
116 emits its status message at the same speed as specified with
117 (the first) baud_rate value on the command line.
118 Since the -m feature may fail on heavily-loaded systems, you
120 still should enable BREAK processing by enumerating all expected
121 baud rates on the command line.
122 -n Do not prompt the user for a login name. This can be used in
124 connection with -l option to invoke a non-standard login process
125 such as a BBS system. Note that with the -n option, agetty gets
126 no input from user who logs in and therefore won't be able to
127 figure out parity, character size, and newline processing of the
128 connection. It defaults to space parity, 7 bit characters, and
129 ASCII CR (13) end-of-line character. Beware that the program
130 that agetty starts (usually /bin/login) is run as root.
131 -t timeout
133 Terminate if no user name could be read within timeout seconds.
134 This option should probably not be used with hard-wired lines.
135 -L Force the line to be a local line with no need for carrier
137 detect. This can be useful when you have a locally attached ter‐
138 minal where the serial line does not set the carrier detect sig‐
139 nal.
140 -s Try to keep the existing baud rate. The baud rates from the com‐
142 mand line are used when agetty receives a BREAK character.
143 -U Turn on support for detecting an uppercase only terminal. This
145 setting will detect a login name containing only capitals as
146 indicating an uppercase only terminal and turn on some upper to
147 lower case conversions. Note that this has no support for any
148 unicode characters.
149 -w Wait for the user or the modem to send a carriage-return or a
151 linefeed character before sending the /etc/issue (or other) file
152 and the login prompt. Very useful in connection with the -I
153 option.
154
156 This section shows examples for the process field of an entry in the
157 /etc/inittab file. You'll have to prepend appropriate values for the
158 other fields. See inittab(5) for more details.
159 For a hard-wired line or a console tty:
161 /sbin/agetty 9600 ttyS1
162 For a directly connected terminal without proper carriage detect
164 wiring: (try this if your terminal just sleeps instead of giving you a
165 password: prompt.)
166 /sbin/agetty -L 9600 ttyS1 vt100
167 For a old style dial-in line with a 9600/2400/1200 baud modem:
169 /sbin/agetty -mt60 ttyS1 9600,2400,1200
170 For a Hayes modem with a fixed 115200 bps interface to the machine:
172 (the example init string turns off modem echo and result codes, makes
173 modem/computer DCD track modem/modem DCD, makes a DTR drop cause a dis-
174 connection and turn on auto-answer after 1 ring.)
175 /sbin/agetty -w -I 'ATE0Q1&D2&C1S0=1\015' 115200 ttyS1
176
179 The issue-file (/etc/issue or the file set with the -f option) may con‐
180 tain certain escape codes to display the system name, date and time
181 etc. All escape codes consist of a backslash (\) immediately followed
182 by one of the letters explained below.
183 b Insert the baudrate of the current line.
186 d Insert the current date.
188 s Insert the system name, the name of the operating system.
190 l Insert the name of the current tty line.
192 m Insert the architecture identifier of the machine, eg. i486
194 n Insert the nodename of the machine, also known as the hostname.
196 o Insert the NIS domainname of the machine.
198 O Insert the DNS domainname of the machine.
200 r Insert the release number of the OS, eg. 1.1.9.
202 t Insert the current time.
204 u Insert the number of current users logged in.
206 U Insert the string "1 user" or "<n> users" where <n> is the num‐
208 ber of current users logged in.
209 v Insert the version of the OS, eg. the build-date etc.
211 Example: On my system, the following /etc/issue file:
213 This is \n.\o (\s \m \r) \t
215 displays as
217 This is thingol.orcan.dk (Linux i386 1.1.9) 18:29:30
219
223 /var/run/utmp, the system status file.
224 /etc/issue, printed before the login prompt.
225 /dev/console, problem reports (if syslog(3) is not used).
226 /etc/inittab, init(8) configuration file.
227
229 The baud-rate detection feature (the -m option) requires that agetty be
230 scheduled soon enough after completion of a dial-in call (within 30 ms
231 with modems that talk at 2400 baud). For robustness, always use the -m
232 option in combination with a multiple baud rate command-line argument,
233 so that BREAK processing is enabled.
234 The text in the /etc/issue file (or other) and the login prompt are
236 always output with 7-bit characters and space parity.
237 The baud-rate detection feature (the -m option) requires that the modem
239 emits its status message after raising the DCD line.
240
242 Depending on how the program was configured, all diagnostics are writ‐
243 ten to the console device or reported via the syslog(3) facility.
244 Error messages are produced if the port argument does not specify a
245 terminal device; if there is no utmp entry for the current process
246 (System V only); and so on.
247
249 W.Z. Venema <wietse@wzv.win.tue.nl>
250 Eindhoven University of Technology
251 Department of Mathematics and Computer Science
252 Den Dolech 2, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
253 Peter Orbaek <poe@daimi.aau.dk>
255 Linux port and more options. Still maintains the code.
256 Eric Rasmussen <ear@usfirst.org>
258 Added -f option to display custom login messages on different terminals.
259
262 The agetty command is part of the util-linux-ng package and is avail‐
263 able from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
264 AGETTY(8)