Send spawn id exp4 not open error in expect

Figured out why. I had generated ssh keys and copied it on to the destination machine. So there was no "Password: " prompt. Hence before send could complete, the ssh connection had closed.

I deleted the ssh keys from the destination machine and ran the script again and observed no issues

The Error?

spawn telnet too many programs spawned? could not create pipe: too many open files

This error is likely due to your system running out of file handles (or at least exhausting the count available to you).

I suspect the reason for this is abandoned telnet sessions which are left open.

Now let's talk about why they may still be hanging around.

Not Even, Close?

Close may not actually close the telnet connection, especially if telnet doesn't recognize the session has been closed, only expect's session with telnet (See: The close Command). In this case Telnet is most likely being kept alive waiting for more input from the network side and by a TCP keepalive.

Not all applications recognize close, which is presented as an EOF to the receiving application. Because of this they may remain open even when their input has been closed.

Tell "Telnet", It's Over.

In that case, you will need to interrupt telnet. If your intent is to complete some work and exit. Then that is exactly what we'll need to do.

For "telnet" you can cleanly exit by issuing a "send “35\r”" (which would be "ctrl+]" on the keyboard if you had to type it yourself) followed by "quit" and then a carriage return. This will tell telnet to exit gracefully.

Expect script: start telnet, run commands, close telnet Excerpt:

#!/usr/bin/expect
set timeout 1
set ip [lindex $argv 0]
set port [lindex $argv 1]
set username [lindex $argv 2]
set password [lindex $argv 3]
spawn telnet $ip $port
expect “‘^]’.”
send – – “\r”
expect “username:” {
    send – – “$username\r”
    expect “password:”
    send – – “$password\r”
}
expect “$”
send – – “ls\r”
expect “$”
sleep 2
# Send special ^] to telnet so we can tell telnet to quit.
send “35\r”
expect “telnet>”
# Tell Telnet to quit.
send – – “quit\r”
expect eof
# You should also, either call "wait" (block) for process to exit or "wait -nowait" (don't block waiting) for process exit.
wait

Wait, For The Finish.

Expect - The wait Command

Without "wait", expect may sever the connection to the process prematurely, this can cause the creation zombies in some rare cases. If the application did not get our signal earlier (the EOF from close), or if the process doesn't interpret EOF as an exit status then it may also continue running and your script would be none the wiser. With wait, we ensure we don't forget about the process until it cleans up and exits.

Otherwise, we may not close any of these processes until expect exits. This could cause us to run out of file handles if none of them close for a long running expect script (or one which connects to a lot of servers). Once we run out of file handles, expect and everything it started just dies, and you won't see those file handles exhausted any longer.

Timeout?, Catch all?, Why?

You may also want to consider using a "timeout" in case that the server doesn't respond when expected so we can exit early. This is ideal for severely lagged servers which should instead get some admin attention.

Catch all can help your script deal with any unexpected responses that don't necessarily prevent us from continuing. We can choose to just continue processing, or we could choose to exit early.

Expect Examples Excerpt:

expect {           
    "password:" {
        send "password\r"
    } "yes/no)?" {
        send "yes\r"
        set timeout -1
    } timeout {
        exit
    # Below is our catch all
    } -re . {
        exp_continue
    #
    } eof {
        exit
    }
}