Well, I am using AIX version 4. I tried a similar
test and I was able to change and save /etc/hosts.
Perhaps there is a difference right there between
AIX and FreeBSD. As a matter of facts, I will
attach below a copy of the program that I am writing.
Perhaps someone can make suggestions.
The program will provide remote printing support to a
Windows/98 ws with a printer attached to it, managed
by a lpd server. The user comes in via a VPN that
provides a different IP address with every connection.
That’s the reason to update the /etc/hosts table.
If anyone knows an off the shelv software that will do
this then I will recommend that to the client. Althoug
it is more fun to write it myself as I learn ruby.
Of course I am not providing ALL the details, such us
the AIX printer config, which I think is irrelevant at
this point. For the UDP part I used a piece of code
from “The Ruby Way”.
Thank you
Here is the ruby code:
require “socket”
log=“/tmp/udpsrv.log”
begin
out = File.new(log, “a”)
rescue => e
puts “Problem with I/O operation: #{e}”
exit 1
else
time = Time.now
time1 = time.strftime(“%a%b%d%Y %H:%M:%S”)
out.puts time1 + " " + $0 + " Started Executing…"
PORT = 12321
time = Time.now
time1 = time.strftime(“%a%b%d%Y %H:%M:%S”)
out.puts time1 + " Listening on port: " + PORT.to_s
server = UDPSocket.open # Using UDP here…
server.bind(“cwsa”, PORT)
out.close
loop do
puts “Waiting for requests”
out = File.new(log, “a”)
time = Time.now
time1 = time.strftime(“%a%b%d%Y %H:%M:%S”)
out.puts time1 + " Wait for requests."
text, sender = server.recvfrom(64)
time = Time.now
time1 = time.strftime("%a%b%d%Y %H:%M:%S")
out.puts time1 + " Client domain: " +
sender[0].to_s
out.puts time1 + " Client port: " +
sender[1].to_s
out.puts time1 + " Client host: " +
sender[2].to_s
out.puts time1 + " Client IP adddress: " +
sender[3].to_s
out.puts time1 + " Client requests: " + text.to_s
system("rm /tmp/newhosts 1>/dev/null 2>&1") #
Remove old file
function, printer = text.chomp.split
if function.include?(“Enable”)
# Replace old definition from /etc/hosts table
entry for this printer
fileArr = IO.readlines(“/tmp/hosts”)
f = File.new(“/tmp/newhosts”, “w+”)
index = 0
found = false
fileArr.each do |line|
if line.include?(“VPNTEST”)
fileArr[index] = sender[3].to_s + " " +
“VPNTEST”
found = true
break
end
index += 1
end # End of do loop
if !found # Add to end of hosts file, if it
was not found
f.close # Firts close file
entry = sender[3].to_s + " " + “VPNTEST”
#system(“echo #{entry} >> /tmp/hosts”)
system(“mv /tmp/hosts /etc/hosts”) #
UNCOMMENT
else # Re-write hosts file back with the change IP
address
f.puts fileArr
f.close
#system(“mv /tmp/newhosts /tmp/hosts”)
system(“mv /tmp/newhosts /etc/hosts”)
end
system("enable VPNTEST >>/tmp/dpsrv.log
2>>/tmp/udpsrv.log")
else
if function.include?(“Disable”)
system(“disable VPNTEST >>/tmp/dpsrv.log
2>>/tmp/udpsrv.log”)
else
out.puts time1 + " Request " + text.to_s + "
ignored."
end
end
out.close
end
end
···
— Brian Candler B.Candler@pobox.com wrote:
On Sat, Jul 26, 2003 at 08:57:00PM +0900, Ludwigi > Beethoven wrote:
I guess I would have to grab the file and update
it
rather quickly, and hope that nobody else is
updating
it at the same time via some other way.
The requirement was to prevent another user editing
the same file with ‘vi’,
right?
On my system (FreeBSD), if I edit a file with vi,
then try to edit the same
file in vi in another window, I get:
/etc/motd already locked, session is read-only.
/etc/motd: unmodified, readonly: line 1
This implies that there is some sort of locking
going on.
Now, if I run this test program:
def testlock(filename)
f = File.open(filename)
f.flock(File::LOCK_EX)
sleep 30
f.close
end
testlock(“/etc/motd”)
then vi /etc/motd also reports that the file is
locked. Is that not the case
for you?
If not, then the “update it rather quickly and hope”
is most safely done by:
- creating a copy of the file with a different name
and modified contents
- doing a ‘rename’ operation to replace the original
file with it
This is an atomic operation - it will either succeed
or fail. Of course
someone else who has it open in a buffer could
overwrite it again, but at
least it will always be a complete and valid file,
not corrupted by two
people writing to it simultaneously.
Regards,
Brian.
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