|Working on a remote HPC system||
|Navigating Files and Directories||
|Accessing software via Modules||
|Using resources effectively||
|Writing good code||
|What is Parallel Computing||
Quick Reference or “Cheat Sheets” for Queuing System Commands
Search online for the one that fits you best, but here’s some to start:
- Slurm summary from SchedMD
- Torque/PBS summary from Iowa State
- Translating between Slurm and PBS from University of Minnesota
Units and Language
A computer’s memory and disk are measured in units called Bytes (one Byte is 8 bits). As today’s files and memory have grown to be large given historic standards, volumes are noted using the SI prefixes. So 1000 Bytes is a Kilobyte (kB), 1000 Kilobytes is a Megabyte (MB), 1000 Megabytes is a Gigabyte (GB), etc.
History and common language have however mixed this notation with a different meaning. When people say “Kilobyte”, they mean 1024 Bytes instead. In that spirit, a Megabyte is 1024 Kilobytes.
To address this ambiguity, the International System of Quantities standardizes the binary prefixes (with base of 210=1024) by the prefixes Kibi (ki), Mebi (Mi), Gibi (Gi), etc. For more details, see here.
“No such file or directory” or “symbol 0096” Errors
rsync may throw a perplexing error about files that very much do
exist. One source of these errors is copy-and-paste of command line arguments
from Web browsers, where the double-dash string
-- is rendered as an em-dash
character “—” (or en-dash “–”, or horizontal bar
―). For example,
instead of showing the transfer rate in real time, the following command fails
[user@laptop ~]$ rsync —progress my_precious_data.txt yourUsername@nesi.org.nz rsync: link_stat "/home//—progress" failed: No such file or directory (2) rsync error: some files/attrs were not transferred (see previous errors) (code 23) at main.c(1207) [sender=3.1.3]
The correct command, different only by two characters, succeeds:
[user@laptop ~]$ rsync --progress my_precious_data.txt yourUsername@nesi.org.nz
We have done our best to wrap all commands in code blocks, which prevents this subtle conversion. If you encounter this error, please open an issue or pull request on the lesson repository to help others avoid it.
Transferring Files Interactively With
scp is useful, but what if we don’t know the exact location of what we want
to transfer? Or perhaps we’re simply not sure which files we want to transfer
sftp is an interactive way of downloading and uploading files. Let’s
connect to a cluster, using
sftp – you’ll notice it works the same way
[user@laptop ~]$ sftp yourUsername@remote.computer.address
This will start what appears to be a bash shell (though our prompt says
sftp>). However we only have access to a limited number of commands. We can
see which commands are available with
Available commands: bye Quit sftp cd path Change remote directory to 'path' chgrp grp path Change group of file 'path' to 'grp' chmod mode path Change permissions of file 'path' to 'mode' chown own path Change owner of file 'path' to 'own' df [-hi] [path] Display statistics for current directory or filesystem containing 'path' exit Quit sftp get [-afPpRr] remote [local] Download file reget [-fPpRr] remote [local] Resume download file reput [-fPpRr] [local] remote Resume upload file help Display this help text lcd path Change local directory to 'path' lls [ls-options [path]] Display local directory listing lmkdir path Create local directory ln [-s] oldpath newpath Link remote file (-s for symlink) lpwd Print local working directory ls [-1afhlnrSt] [path] Display remote directory listing # omitted further output for clarity
Notice the presence of multiple commands that make mention of local and remote. We are actually connected to two computers at once (with two working directories!).
To show our remote working directory:
Remote working directory: /global/home/yourUsername
To show our local working directory, we add an
l in front of the command:
Local working directory: /home/jeff/Documents/teaching/hpc-intro
The same pattern follows for all other commands:
lsshows the contents of our remote directory, while
llsshows our local directory contents.
cdchanges the remote directory,
lcdchanges the local one.
To upload a file, we type
put some-file.txt (tab-completion works here).
sftp> put config.toml
Uploading config.toml to /global/home/yourUsername/config.toml config.toml 100% 713 2.4KB/s 00:00
To download a file we type
sftp> get config.toml
Fetching /global/home/yourUsername/config.toml to config.toml /global/home/yourUsername/config.toml 100% 713 9.3KB/s 00:00
And we can recursively put/get files by just adding
-r. Note that the
directory needs to be present beforehand.
sftp> mkdir content sftp> put -r content/
Uploading content/ to /global/home/yourUsername/content Entering content/ content/scheduler.md 100% 11KB 21.4KB/s 00:00 content/index.md 100% 1051 7.2KB/s 00:00 content/transferring-files.md 100% 6117 36.6KB/s 00:00 content/.transferring-files.md.sw 100% 24KB 28.4KB/s 00:00 content/cluster.md 100% 5542 35.0KB/s 00:00 content/modules.md 100% 17KB 158.0KB/s 00:00 content/resources.md 100% 1115 29.9KB/s 00:00
To quit, we type