mscp/doc/mscp.1.in

.TH MSCP 1 "@MSCP_BUILD_VERSION@" "mscp" "User Commands"

.SH NAME
mscp \- copy files over multiple SSH connections

.SH SYNOPSIS

.B mscp
.RB [ \-vqDpHdNh ]
[\c
.BI \-n \ NR_CONNECTIONS\c
]
[\c
.BI \-m \ COREMASK\c
]
[\c
.BI \-u \ MAX_STARTUPS\c
]
[\c
.BI \-I \ INTERVAL\c
]
[\c
.BI \-s \ MIN_CHUNK_SIZE\c
]
[\c
.BI \-S \ MAX_CHUNK_SIZE\c
]
[\c
.BI \-a \ NR_AHEAD\c
]
[\c
.BI \-b \ BUF_SIZE\c
]
[\c
.BI \-l \ LOGIN_NAME\c
]
[\c
.BI \-P \ PORT\c
]
[\c
.BI \-F \ CONFIG\c
]
[\c
.BI \-i \ IDENTITY\c
]
[\c
.BI \-c \ CIPHER\c
]
[\c
.BI \-M \ HMAC\c
]
[\c
.BI \-C \ COMPRESS\c
]
.I source ... target

.SH DESCRIPTION

.PP
.B mscp
copies files over multiple SSH (SFTP) connections by multiple
threads. It enables transferring (1) multiple files simultaneously and
(2) a large file in parallel, reducing the transfer time for a lot
of/large files over networks.

.PP
The usage of
.B mscp
imitates the
.B scp
command of
.I OpenSSH,
for example:

.nf
    $ mscp srcfile user@example.com:dstfile
.fi

Remote hosts only need to run standard
.B sshd
supporting the SFTP subsystem, and users need to be able to
.B ssh
to the hosts as usual.
.B mscp
does not require anything else.

.PP
.B mscp
uses
.UR https://\:www\:.libssh\:.org
libssh
.UE
as its SSH implementation. Thus, supported SSH features, for example,
authentication, encryption, and various options in ssh_config, follow
what
.I libssh
supports.

.SH OPTIONS
.TP
.B \-n \fINR_CONNECTIONS\fR
Specifies the number of SSH connections. The default value is
calculated from the number of CPU cores on the host with the following
formula: floor(log(nr_cores)*2)+1.

.TP
.B \-m \fICOREMASK\fR
Configures CPU cores to be used by the hexadecimal bitmask.  All CPU
cores are used by default.

.TP
.B \-u \fIMAX_STARTUPS\fR
Specifies the number of concurrent outgoing SSH connections.
.B sshd
limits the number of simultaneous SSH connection attempts by
.I MaxStartups
in
.I sshd_config.
The default
.I MaxStartups
is 10; thus, we set the default MAX_STARTUPS 8.

.TP
.B \-I \fIINTERVAL\fR
Specifies the interval (in seconds) between SSH connection
attempts. Some firewall products treat SSH connection attempts from a
single source IP address for a short period as a brute force attack.
This option inserts intervals between the attempts to avoid being
determined as an attack. The default value is 0.

.TP
.B \-s \fIMIN_CHUNK_SIZE\fR
Specifies the minimum chunk size.
.B mscp
divides a file into chunks and copies the chunks in parallel.

.TP
.B \-S \fIMAX_CHUNK_SIZE\fR
Specifies the maximum chunk size. The default is file size divided by
the number of connections.

.TP
.B \-a \fINR_AHEAD\fR
Specifies the number of inflight SFTP commands. The default value is
32.

.TP
.B \-b \fIBUF_SIZE\fR
Specifies the buffer size for I/O and transfer over SFTP. The default
value is 16384. Note that the SSH specification restricts buffer size
delivered over SSH. Changing this value is not recommended at present.

.TP
.B \-v
Increments the verbose output level.

.TP
.B \-q
Quiet mode: turns off all outputs.

.TP
.B \-D
Dry-run mode: it scans source files to be copied, calculates chunks,
and resolves destination file paths. Dry-run mode with
.B -vv
option enables confirming files to be copied and their destination
paths.

.TP
.B \-r
No effect.
.B mscp
copies recursively if a source path is a directory. This option exists
for just compatibility.

.TP
.B \-l \fILOGIN_NAME\fR
Specifies the username to log in on the remote machine as with
.I ssh(1).

.TP
.B \-P \fIPORT\fR
Specifies the port number to connect to on the remote machine as with
ssh(1) and scp(1).

.TP
.B \-F \fICONFIG\fR
Specifies an alternative per-user ssh configuration file. Note that
acceptable options in the configuration file are what
.I libssh
supports.

.TP
.B \-i \fIIDENTITY\fR
Specifies the identity file for public key authentication.

.TP
.B \-c \fICIPHER\fR
Selects the cipher to use for encrypting the data transfer. See
.UR https://\:www\:.libssh\:.org/\:features/
libssh features
.UE .

.TP
.B \-M \fIHMAC\fR
Specifies MAC hash algorithms. See
.UR https://\:www\:.libssh\:.org/\:features/
libssh features
.UE .

.TP
.B \-C \fICOMPRESS\fR
Enables compression: yes, no, zlib, zlib@openssh.com. The default is
none. See
.UR https://\:www\:.libssh\:.org/\:features/
libssh features
.UE .

.TP
.B \-p
Preserves modification times and access times (file mode bits are
preserved by default).

.TP
.B \-H
Disables hostkey checking.

.TP
.B \-d
Increments the ssh debug output level.

.TP
.B \-N
Enables Nagle's algorithm. It is disabled by default.

.TP
.B \-h
Prints help.

.SH EXIT STATUS
Exit status is 0 on success,  and >0 if an error occurs.

.SH ENVIRONMENT

.PP
.B mscp
recognizes the following environment variables.

.TP
.B MSCP_SSH_AUTH_PASSWORD
This environment variable passes a password for password
authentication to establish SSH connections.

.TP
.B MSCP_SSH_AUTH_PASSPHRASE
This environment variable passes a passphrase for public-key
authentication for establishing SSH connections.



.SH NOTES

.PP
.B mscp
uses glob(3) for globbing pathnames, including matching patterns for
local and remote paths. However, globbing on the
.I remote
side does not work with musl libc (used in Alpine Linux and the
single-binary version of mscp) because musl libc does not support
GLOB_ALTDIRFUNC.

.PP
.B mscp
does not support remote-to-remote copy, which
.B scp
supports.

.SH EXAMPLES

.PP
Copy a local file to a remote host with different name:

.nf
    $ mscp ~/src-file 10.0.0.1:copied-file
.fi

.PP
Copy a local file and a directory to /tmp at a remote host:

.nf
    $ mscp ~/src-file dir1 10.0.0.1:/tmp
.fi

.PP
In a long fat network, following options might improve performance:

.nf
    $ mscp -n 64 -m 0xffff -a 64 -c aes128-gcm@openssh.com src 10.0.0.1:
.fi

.B -n
increases the number of SSH connections than default,
.B -m
pins threads to specific CPU cores,
.B -a
increases asynchronous inflight SFTP WRITE/READ commands, and
.B -c aes128-gcm@openssh.com
will be faster than the default chacha20-poly1305 cipher, particularly
on hosts that support AES-NI.



.SH "SEE ALSO"
.BR scp (1),
.BR ssh (1),
.BR sshd (8).

.SH "PAPER REFERENCE"


Ryo Nakamura and Yohei Kuga. 2023. Multi-threaded scp: Easy and Fast
File Transfer over SSH. In Practice and Experience in Advanced
Research Computing (PEARC '23). Association for Computing Machinery,
New York, NY, USA, 320–323.
.UR https://\:doi\:.org/\:10.1145/\:3569951.3597582
DOI
.UE .


.SH CONTACT INFROMATION
.PP
For pathces, bug reports, or feature requests, please open an issue on
.UR https://\:github\:.com/\:upa/\:mscp
GitHub
.UE .

.SH AUTHORS
Ryo Nakamura <upa@haeena.net>