I need to create a small utility. Using Java, remotely (from another machine) I need to search for files (whether particular files exist or not). I would know exact names of files, or if not, I would know their partial names (so I will be using wildcards).
The problem is: I cannot install anything on that machine (it's a corporate box), but I am allowed FTP, Telnet, SSH login, etc. I would not want to use FTP because there are hundreds of directories and there's no way to know ahead of time where the files are each time (using ftp command LS on each directory every time is simply unproductive). So the best would be to use internal unix 'find' command. Or a similar approach.
I need the best solution to the problem: how can I search for files (from hundreds of thousands files in many different folders) remotely on another machine.
Jsch will allow you to connect quite easily to a remote machine and execute operations using SSH. There is not a lot of documentation, but these examples shows about everything you can do, from basic Shell operations to SFTP and much more.
You can locally exec ssh and have it execute the find command on another machine.
e.g.
ssh user#host "find /home/foo -name index.*"
You can exec that from within the JVM and read the output from the process.
Related
I have a program right now that uses the "net use" command to access a shared drive on a network computer at my work. This works fabulously and I'm able to copy a file from the remote machine onto my own using the FileUtil library from apache. Now I'm wanting to run batch file located on the remote machine and I want it executed in that environment not my own local machine. At first I thought I could just use the "net use" command again with no problem but when I execute the batch file, it is run on my own machine not the remote one. However, this is not what I want to happen.
So, is anyone familiar with this process of executing batch files on remote machines. Better yet, from inside Java.
Thank you for any feed back I greatly appreciate it!
I don't know much about java but can you execute external programs from it? If the answer is "yes" you might try with PSEXEC from Sysinternals it runs every kind of things remotely.
Ok, so I have a couple of Java programs that I'm running using a chron job on a linux server. These jobs run every ten minutes or so, take literally two minutes to run, and then exit. I need to add a way for the programs to detect, when they start up, if there is already an instance of themselves running, and if so to exit without going any further. I'm really not sure of the best way to handle this though and am hoping someone can offer some advice.
One approach I've considered is to run a command line argument from the java code that does some sort of PS command and looks through those to see if it's running. This seems pretty finicky and complex though for something so small. Plus, I'm not all that knowledgeable with linux and am not even sure the best way to do that. If anyone has some better thoughts, please let me know. Or if that is the best way, if you could provide the linux commands I'd need I'd appreciate it. Thanks.
If you have a writable /tmp directory you can use a lockfile.
When your Java program starts up, check for a file with a name unique to your application (e.g. "my-lock-file.lock") in the /tmp directory. If none exists, create one, and remove it when you're done. If one exists, just exit.
You can check the existence of a file with the .exists() method of the java.io.File class.
If your code needs to be portable, you can use System.getProperty("java.io.tmpdir")); to get an appropriate temporary directory for the platform your code is running on.
You could look at JMX and the Attach API to query for running JVMs.
Or, as Andrew logvinov mentioned, by using a lock file.
If you are using Java WebStart, there's already native support for this.
Many programs solve this by creating a temporary file that points to their PID (often referred to as a "lock" file). The filename should encode all relevant information to distinguish this process from other processes that could legitimately run in parallel.
For example, if the process is bound to a user, it should contain the user name. If the process is bound to a machine, it should (also) contain the hostname (if you put it in machine-bound temp. directory, this is debatable. If you put it in a home directory, think of the case of multiple machines sharing a home via NFS).
The location of these files is typically /tmp. This is a great location, as /tmp is typically wiped during system boot, so no orphan files are left in case of a system crash. Another solution employed by some programs is to put the lock file in the user settings directory, if it is related to the settings. E.g. mozilla thunderbird has a file called /home/<username>/.thunderbird/<profilename>.default/lock.
The file should contain the PID of the process. The idea is simple: If the file contains the PID, it is easy to check whether this process is indeed still running. So if the process crashes, the file gets orphaned. The new process instance will check the PID in the file, see that it is not running any more, and ignore the file (overwrite).
Putting it all together, you could create a file like this:
/tmp/myawesomeservice-username-hostname-lock
With the content:
12345
hi
i want to perform operations on files like rename, copy and etc.
these are not local files. they are located on remote computers.
I have 2 options:
1. run some kind of a telnet client (a framework that i already have in my system) from the java code. connect to the remote computer and perform a cmd operation.
2. perform a regular java.io operation on the remote path.
the problem with 1 is that its not cross platform (only theoretical problem for me), and that i generally dont want to use this telnet framework.
the problem with 2 is that large operations on remote files is slower, compared to same operation being performed on the machine itself with telnet.
am i right?
any other options?
any additional inputs?
thanks.
If you can deploy your application to the remote computer, you can simply write your own little client and server for these file operations.
I have here a Windows distribution server that runs an ANT task to build enterprise software. What I need to do is to have the ANT task copy and run a VM image (Linux), and then...talk to that Linux VM through the host operating system (through the ant task itself). We need to be able to send files and/or commands to it.
Is there a practical way to go about this? I know that we already have a way to send commands to VMs that are also running Windows (so windows-windows interaction) -- but is there a way to do a windows-linux interaction?
I've implemented the thing you wanted. Of course, for my own purposes, and then just found this question by googling on keywords "vmware" and "ant".
https://github.com/zhuravlik/ant-vix-tasks
This is the taskset for Ant to manage VMWare VMs.
It works via VIX API, so Linux guests should be supported by it.
I did not test it with VMWare Server, though. Only with Workstation.
But the API is common, so it should work.
Using ssh is probably the simplest. There is an ant task for that. Scp task is also there to copy files
It will depend on what you need to do, but:
The Linux system could expose an SSH server, and the host can do just about anything it needs to via SSH.
The Linux system could expose a web service that the host consumes.
The Linux system could expose a Samba share which the host then connects to and reads/writes from (if all you need to do is deal with some files, but that seems unlikely).
There are probably dozens of options.
I'm creating a test which will perform some stress testing of the app which talks to a Postgres database. In order to make it replicable I'd like to recreate the database on every run. Startup method decorated with org.junit.Before annotation will drop the database (if it exists) and restore it from a dump file. Doing this form shell/command is trivial:
psql -f db.out newdb
or something along these lines. Since the test may be performed on a JVM that's not running on the same machine which hosts the database I'm wondering if it's possible to invoke shell/batch script on remote machine from Java programmaticaly.
Thanks
If you have knowledge of the machine details (hostname, login, password) the only thing I can think of at the moment is using a Java SSH library to login to the box and run that command.
Or you could write a script on your local machine which ran the script on the remote machine given the correct parameters.
That's the simplest way I can think of anyway!
If setting up SSH is too complex, you can write a small Java program which listens for connections on a socket and then runs the script. Install that on the Postgres server and connect to it in the test case.
That said, I suggest to install a copy of Postgres on every developer machine. That would make your tests run much faster and you wouldn't get spurious errors when two developers run the tests at the same time. Also, you won't have errors because of network problems, because someone does maintenance on the server, because developer X has changed the DB schema, etc. etc.