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Top Forums Shell Programming and Scripting Unix script (sh): state of ftp process Post 302320156 by pludi on Wednesday 27th of May 2009 07:34:23 AM
Old 05-27-2009
No, your sleep does not block the FTP command. Let's sidetrack into kernel process management for a bit:

Since their invention CPU cores can only execute one process at a time. This meant that a single process waiting for user input could block the whole system. So someone came up with the idea of time slices. Each process is allowed execution for a certain time. After that time it returns control to the kernel. All was good until some processes didn't return control on purpose.
Most modern kernels use preempting instead. Again, each process is allocated execution time. After that time the OS kernel is woken via a timer interrupt (or sooner if the process gives it's rights back because it's waiting for something), the first process is sent into a sleep mode and another is given CPU time. The first process will continue when it's its turn.

Now back to your case: you're starting the FTP process and send it into the background. It gets its time-slices just like any other process, but it's not executing the whole time. Sometimes other processes are executed, so ftp is marked as 'sleeping' or, better said, waiting for its turn again. If you only have one CPU core and get the current list with ps, all processes except for ps will (most likely) be marked as 'sleeping', since ps is currently using its allocated time to gather the stats.

My suggestion for your problem would be:
  1. ping the host in question (maybe mark those pingable accordingly and skip the others)
  2. test if the FTP port is open. You can either use netcat (eg: netcat -z $host 21 and check $?) or parse the output of nmap)
  3. create a small checkfile on the FTP server, and fetch that first. For example, start the FTP command for that in the background. If it's still running after 5 seconds, consider the host dead.
  4. if all (necessary) checks are good, continue with the large transfer
 

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netrc(4)							   File Formats 							  netrc(4)

NAME
netrc - file for ftp remote login data DESCRIPTION
The .netrc file contains data for logging in to a remote host over the network for file transfers by ftp(1). This file resides in the user's home directory on the machine initiating the file transfer. Its permissions should be set to disallow read access by group and oth- ers. See chmod(1). Tokens can be separated by SPACE, TAB, or NEWLINE characters. The following tokens are supported: account string Supply an additional account password. If this token is present, the auto-login process supplies the specified string if the remote server requires an additional account password. If the remote server does not require an additional account password, the auto-login process initiates an ACCT command. default Same as machine name, except that default matches any name. There can be only one default token, and it must be after all machine tokens. The default token is normally used as follows: default login anonymous password user@site Such an entry gives the user automatic anonymous ftp login to machines not specified in .netrc. login name Identify a user on the remote machine. If this token is present, the auto-login process initiates a login using the specified name. machine name Identify a remote machine name. The auto-login process searches the .netrc file for a machine token that matches the remote machine specified on the ftp command line or as an open command argument. Once a match is made, the subsequent .netrc tokens are processed, stopping when the EOF is reached or another machine token is encountered. macdef name Define a macro. This token functions the same as ftp macdef. A macro is defined with the specified name; its contents begin with the next .netrc line and continue until a null line (consecutive NEWLINE characters) is encountered. If a macro named init is defined, it is automatically executed as the last step in the auto-login process. password string Supply a password. If this token is present, the auto-login process supplies the specified string if the remote server requires a password as part of the login process. If this token is present in the .netrc file, ftp aborts the auto-login process if the .netrc is readable by anyone besides the user. skipsyst Skip the SYST command that is sent by default to all remote servers upon connection. The system command is what enables the automatic use of binary mode rather than the protocol default ascii mode. As some older servers cannot handle the ftp command, this directive is provided to allow inter-operability with these servers. EXAMPLES
Example 1 A Sample .netrc File A .netrc file containing the following line: machine ray login demo password mypassword allows an autologin to the machine ray using the login name demo with password mypassword. FILES
~/.netrc SEE ALSO
chmod(1), ftp(1), in.ftpd(1M) SunOS 5.11 25 Aug 2006 netrc(4)
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