I still pause to remember that I have to type 'if=' and 'of=' and 'bs=' instead ...

code_duck · on June 16, 2018

What always gets me is ssh, scp and sftp... having to specify oPort= for sftp compared to -p for ssh.

trinitry3 · on June 16, 2018

You can use -P.

kasey_junk · on June 16, 2018

Whoever made it -p in ssh & -P in scp can fuck right off.

cesarb · on June 16, 2018

The reason is that scp was designed as a secure replacement for rcp, which was designed as a remote version of cp. The flags -p and -r were inherited from cp by rcp (see https://linux.die.net/man/1/rcp), so for compatibility scp had to use the same flags.

As for ssh, I haven't looked at its history, but I suspect it's older than scp; the intuitive flag for "port" is -p, so that's what ssh used.

code_duck · on June 17, 2018

Good to know. I wonder if that's a recent improvement? Last time I was doing lots of sysadmin work was 2011.

pronoiac · on June 16, 2018

I'd prefer ddrescue or just pv, just for the progress meter, and saner arguments.

dmartinez · on June 16, 2018

`tldr`[0] can be helpful for quick references like this. I never worry about commands like `ssh` anymore because of this. This is the output for `dd`:

$ tldr dd

dd

Convert and copy a file.

- Make a bootable usb drive from an isohybrid file (such like archlinux-xxx .iso):

    dd if=file.iso of=/dev/usb_drive

- Clone a drive to another drive with 4MB block and ignore error:

    dd if=/dev/source_drive of=/dev/dest_drive bs=4m conv=noerror

- Generate a file of 100 random bytes by using kernel random driver:

    dd if=/dev/urandom of=random_file bs=100 count=1

- Benchmark the write performance of a disk:

    dd if=/dev/zero of=file_1GB bs=1024 count=1000000

[0]: https://github.com/tldr-pages/tldr

I_complete_me · on June 17, 2018

I've been using a similar command called 'cheat' [pip install cheat] which does more or less the same thing. I wonder which of the two is more comprehensive. How would I check this efficiently?