Communications Commands

  • biff – Mail notification
  • comstat – Incoming mail daemon
  • Mail.rc – Configuration file for mail
  • wall – Send message to all users
  • write – Send messages to specific user
  • mesg – allow/disallow write or talk
  • ate – vt100 terminal emulator
  • cu – Connect to unix system
  • uucp – Copy files to unix system
  • uux – Execute a command on another unix system
  • sendmail – Deamon for sending email
  • aliases – Alternate email addresses


Used to dial a modem and connect to another computer. Uses vt100 emulation. Allows for transfering of files.

Default files:

  • /usr/lib/dir – directory of phone numbers
  • /usr/lib/ate.def – contains default parameters. An ate.def Is copied to your current path when ate is executed.


Enable/disables mail notification during current display session. Works in conjunction
with the comstat daemon.

Examples What it does
biff y Enables mail notification
biff n Disables mail notification

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Daemon that will notify users of incoming mail. The first seven lines or 560 characters of the message is displayed. Make sure the /etc/inetd.conf file has the comsat entry uncommented so that the inetd daemon can invoke it.

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The file /usr/share/lib/Mail.rc contains default settings when using standard mail command.
Useful settings…

  • setaskcc
  • autoprint
  • dot
  • set crt=20
  • set PAGER=pg

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cu (connect unix) is a terminal emulator that connects to a local or remote system. If connecting to another UNIX system, you can also perform file transfers.

Examples What it does
cu -d ibm -d option is used to run in debug mode. The debug option is useful to determine if your able to talk to the modem, able to dial out the modem or to connect to the remote machine. This will try to contact the node named ibm. The ibm entry is found in the /usr/lib/uucp/Systems file. Also the file named /usr/lib/uucp/Devices will specify which port that ibm will use to call-out.
take Takes file from remote host (called to) to local host (called from)
put Takes files from local host (called from) to remote host (called to)
~%b Generates a BREAK signal

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Allows/disallows ‘write’ or ‘talk’ session to display terminal

Examples What it does
mesg y Allows ‘write’ or ‘talk’
mesg n Doesn’t allows ‘write’ or ‘talk’

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Copies file(s) from one unix system to another.

Example: uucp -x9 /u/roger/daily.log rs520!/u/log

Copies the daily.log file found on the local machine to the /u/log directory on the remote machine named rs520.

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Executes an command on another system.

Example: uux -z rs520!lp /u/roger/memo.log

The local file named /u/roger/memo.log will be printed on the remote node named rs520. The -z option will notify the user if the command completed successfully.

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Writes a message to all the users that are currently logged in. This command is typically used by the system administrator to notify users that the system will be coming down shortly for maintenance or system updates.


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Allows two logged-in users to have an interactive chat session with each other. Consult the mesg command to disable the ‘talk’ or ‘write’ command from writing to your terminal.
Must have ‘/etc/writesrv’ daemon running if you wish to have the ability to write to other users.

Examples What it does
write roger Start a conversation with the user roger
write – tty22 Start a conversation with the person logged in on terminal 22

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The daemon that is is used to control the sending of Email.

Examples What it does
sendmail -bp Displays any Email that is in the send queue.
refresh -s sendmail Will cause the current running daemon to use the current configuration stored in /etc/

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The file etc/aliases contains alternate email addresses to forward email to another user name. After changes are made run the command /usr/sbin/sendmail -bi to recompile the aliases file.

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