1AGETTY(8) System Manager's Manual AGETTY(8)
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6 agetty - alternative Linux getty
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10 agetty [-ihLmnw] [-f issue_file] [-l login_program] [-I init] [-t time‐
11 out] [-H login_host] port baud_rate,... [term]
12 agetty [-ihLmnw] [-f issue_file] [-l login_program] [-I init] [-t time‐
13 out] [-H login_host] baud_rate,... port [term]
14
17 agetty opens a tty port, prompts for a login name and invokes the
18 /bin/login command. It is normally invoked by init(8).
19 agetty has several non-standard features that are useful for hard-wired
21 and for dial-in lines:
22 o Adapts the tty settings to parity bits and to erase, kill, end-
24 of-line and uppercase characters when it reads a login name.
25 The program can handle 7-bit characters with even, odd, none or
26 space parity, and 8-bit characters with no parity. The following
27 special characters are recognized: @ and Control-U (kill); #,
28 DEL and back space (erase); carriage return and line feed (end
29 of line).
30 o Optionally deduces the baud rate from the CONNECT messages pro‐
32 duced by Hayes(tm)-compatible modems.
33 o Optionally does not hang up when it is given an already opened
35 line (useful for call-back applications).
36 o Optionally does not display the contents of the /etc/issue file.
38 o Optionally displays an alternative issue file instead of
40 /etc/issue.
41 o Optionally does not ask for a login name.
43 o Optionally invokes a non-standard login program instead of
45 /bin/login.
46 o Optionally turns on hard-ware flow control
48 o Optionally forces the line to be local with no need for carrier
50 detect.
51 This program does not use the /etc/gettydefs (System V) or /etc/get‐
53 tytab (SunOS 4) files.
54
56 port A path name relative to the /dev directory. If a "-" is speci‐
57 fied, agetty assumes that its standard input is already con‐
58 nected to a tty port and that a connection to a remote user has
59 already been established.
60 Under System V, a "-" port argument should be preceded by a
62 "--".
63 baud_rate,...
65 A comma-separated list of one or more baud rates. Each time
66 agetty receives a BREAK character it advances through the list,
67 which is treated as if it were circular.
68 Baud rates should be specified in descending order, so that the
70 null character (Ctrl-@) can also be used for baud rate switch‐
71 ing.
72 term The value to be used for the TERM environment variable. This
74 overrides whatever init(8) may have set, and is inherited by
75 login and the shell.
76
78 -h Enable hardware (RTS/CTS) flow control. It is left up to the
79 application to disable software (XON/XOFF) flow protocol where
80 appropriate.
81 -i Do not display the contents of /etc/issue (or other) before
83 writing the login prompt. Terminals or communications hardware
84 may become confused when receiving lots of text at the wrong
85 baud rate; dial-up scripts may fail if the login prompt is pre‐
86 ceded by too much text.
87 -f issue_file
89 Display the contents of issue_file instead of /etc/issue. This
90 allows custom messages to be displayed on different terminals.
91 The -i option will override this option.
92 -I initstring
94 Set an initial string to be sent to the tty or modem before
95 sending anything else. This may be used to initialize a modem.
96 Non printable characters may be sent by writing their octal code
97 preceded by a backslash (\). For example to send a linefeed
98 character (ASCII 10, octal 012) write \012.
99 -l login_program
101 Invoke the specified login_program instead of /bin/login. This
102 allows the use of a non-standard login program (for example, one
103 that asks for a dial-up password or that uses a different pass‐
104 word file).
105 -H login_host
107 Write the specified login_host into the utmp file. (Normally, no
108 login host is given, since agetty is used for local hardwired
109 connections and consoles. However, this option can be useful for
110 identifying terminal concentrators and the like.
111 -m Try to extract the baud rate the CONNECT status message produced
113 by Hayes(tm)-compatible modems. These status messages are of the
114 form: "<junk><speed><junk>". agetty assumes that the modem
115 emits its status message at the same speed as specified with
116 (the first) baud_rate value on the command line.
117 Since the -m feature may fail on heavily-loaded systems, you
119 still should enable BREAK processing by enumerating all expected
120 baud rates on the command line.
121 -n Do not prompt the user for a login name. This can be used in
123 connection with -l option to invoke a non-standard login process
124 such as a BBS system. Note that with the -n option, agetty gets
125 no input from user who logs in and therefore won't be able to
126 figure out parity, character size, and newline processing of the
127 connection. It defaults to space parity, 7 bit characters, and
128 ASCII CR (13) end-of-line character. Beware that the program
129 that agetty starts (usually /bin/login) is run as root.
130 -t timeout
132 Terminate if no user name could be read within timeout seconds.
133 This option should probably not be used with hard-wired lines.
134 -L Force the line to be a local line with no need for carrier
136 detect. This can be useful when you have a locally attached ter‐
137 minal where the serial line does not set the carrier detect sig‐
138 nal.
139 -w Wait for the user or the modem to send a carriage-return or a
141 linefeed character before sending the /etc/issue (or other) file
142 and the login prompt. Very useful in connection with the -I
143 option.
144
146 This section shows examples for the process field of an entry in the
147 /etc/inittab file. You'll have to prepend appropriate values for the
148 other fields. See inittab(5) for more details.
149 For a hard-wired line or a console tty:
151 /sbin/agetty 9600 ttyS1
152 For a directly connected terminal without proper carriage detect
154 wiring: (try this if your terminal just sleeps instead of giving you a
155 password: prompt.)
156 /sbin/agetty -L 9600 ttyS1 vt100
157 For a old style dial-in line with a 9600/2400/1200 baud modem:
159 /sbin/agetty -mt60 ttyS1 9600,2400,1200
160 For a Hayes modem with a fixed 115200 bps interface to the machine:
162 (the example init string turns off modem echo and result codes, makes
163 modem/computer DCD track modem/modem DCD, makes a DTR drop cause a dis-
164 connection and turn on auto-answer after 1 ring.)
165 /sbin/agetty -w -I 'ATE0Q1&D2&C1S0=1\015' 115200 ttyS1
166
169 The issue-file (/etc/issue or the file set with the -f option) may con‐
170 tain certain escape codes to display the system name, date and time
171 etc. All escape codes consist of a backslash (\) immediately followed
172 by one of the letters explained below.
173 b Insert the baudrate of the current line.
176 d Insert the current date.
178 s Insert the system name, the name of the operating system.
180 l Insert the name of the current tty line.
182 m Insert the architecture identifier of the machine, eg. i486
184 n Insert the nodename of the machine, also known as the hostname.
186 o Insert the domainname of the machine.
188 r Insert the release number of the OS, eg. 1.1.9.
190 t Insert the current time.
192 u Insert the number of current users logged in.
194 U Insert the string "1 user" or "<n> users" where <n> is the num‐
196 ber of current users logged in.
197 v Insert the version of the OS, eg. the build-date etc.
199 Example: On my system, the following /etc/issue file:
201 This is \n.\o (\s \m \r) \t
203 displays as
205 This is thingol.orcan.dk (Linux i386 1.1.9) 18:29:30
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211 /var/run/utmp, the system status file.
212 /etc/issue, printed before the login prompt.
213 /dev/console, problem reports (if syslog(3) is not used).
214 /etc/inittab, init(8) configuration file.
215
217 The baud-rate detection feature (the -m option) requires that agetty be
218 scheduled soon enough after completion of a dial-in call (within 30 ms
219 with modems that talk at 2400 baud). For robustness, always use the -m
220 option in combination with a multiple baud rate command-line argument,
221 so that BREAK processing is enabled.
222 The text in the /etc/issue file (or other) and the login prompt are
224 always output with 7-bit characters and space parity.
225 The baud-rate detection feature (the -m option) requires that the modem
227 emits its status message after raising the DCD line.
228
230 Depending on how the program was configured, all diagnostics are writ‐
231 ten to the console device or reported via the syslog(3) facility.
232 Error messages are produced if the port argument does not specify a
233 terminal device; if there is no utmp entry for the current process
234 (System V only); and so on.
235
237 W.Z. Venema <wietse@wzv.win.tue.nl>
238 Eindhoven University of Technology
239 Department of Mathematics and Computer Science
240 Den Dolech 2, P.O. Box 513, 5600 MB Eindhoven, The Netherlands
241 Peter Orbaek <poe@daimi.aau.dk>
243 Linux port and more options. Still maintains the code.
244 Eric Rasmussen <ear@usfirst.org>
246 Added -f option to display custom login messages on different terminals.
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250 Sat Nov 25 22:51:05 MET 1989
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253 96/07/20
254 AGETTY(8)