Ssh – Direct stderr to a file over ssh

io-redirectionsshstderr

I am trying to execute a command on a local machine and direct the stderr to a remote machine over ssh. I cannot do

 ssh remote machine "command 2>stderr.log"

because the remote machine doesn't have the correct built to execute the command, and I have to run the command on my local machine. I haven't tried it yet but I am mostly positive that we can't do 2>ssh local machine /dir/stderr.log?

Best Answer

As I understand it, you want to run a command locally but save the stderr output to a remote log file.

Try process substitution:

local_command 2> >(ssh somemachine 'cat >logfile')

Here, >(...) is process substitution. It creates a file-like object from the command in the parens. So, 2> redirects stderr to that file-like object, resulting in the output being saved on the remote machine.

Or, just use plain old redirection:

{ local_command 2>&1 1>&3 | ssh somemachine 'cat >logfile'; } 3>&1

Here, stderr is redirected to stdout so that we can pipe it to ssh. So that stdout does not go to ssh, we redirect it to file handle 3. At the end of the command, file handle 3 is redirected to stdout so that it appears on the terminal.

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Bash SSH Tar – How to Compress a Directory Using Tar/Gz Over SSH to Local Computer

You can do it with an ssh command, just tell tar to create the archive on its standard output:

ssh remote.example.com 'cd /path/to/directory && tar -cf - foo | gzip -9' >foo.tgz

Another approach, which is more convenient if you want to do a lot of file manipulations on the other machine but is overkill for a one-shot archive creation, is to mount the remote machine's filesystem with SSHFS (a FUSE filesystem). You should enable compression at the SSH level.

mkdir ~/net/remote.example.com
sshfs -C remote.example.com:/ ~/net/remote.example.com
tar -czf foo.tgz -C ~/net/remote.example.com/path/to/directory foo

Ssh – Cleanup trap for ssh command on multiple remote hosts

Looks like something for gnu parallel. Try something like this:

function server_ssh() {
  parallel --line-buffer ssh server{} "$1" ::: 01 02 03
}

--line-buffer option is needed to allow mixing output of the different commands together (by default it groups output of each command together, so has to wait until each finishes to display).

-u should work here also. Normally it could allow parts of lines to get mixed up together, but since the commands you're using are likely line-based that shouldn't happen.

Edit: --line-buffer is in alpha testing in the version i have (20130922-1), i'd go with -u.

Best Answer

Related Solutions

Bash SSH Tar – How to Compress a Directory Using Tar/Gz Over SSH to Local Computer

Ssh – Cleanup trap for ssh command on multiple remote hosts

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