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Ryo Nakamura 235ba41c5b default chunk size is filesize/(nr_conn*4) (Issue #20) 
and clean-up chunk_sz related parts.
2024-04-29 19:36:22 +09:00

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.TH MSCP 1 "@MSCP_BUILD_VERSION@" "mscp" "User Commands"
.SH NAME
mscp \- copy files over multiple SSH connections
.SH SYNOPSIS
.B mscp
.RB [ \-46vqDpdNh ]
[\c
.BI \-n \ NR_CONNECTIONS\c
]
[\c
.BI \-m \ COREMASK\c
]
[\c
.BI \-u \ MAX_STARTUPS\c
]
[\c
.BI \-I \ INTERVAL\c
]
[\c
.BI \-W \ CHECKPOINT\c
]
[\c
.BI \-R \ CHECKPOINT\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 \ LIMIT_BITRATE\c
]
[\c
.BI \-l \ LOGIN_NAME\c
]
[\c
.BI \-P \ PORT\c
]
[\c
.BI \-F \ SSH_CONFIG\c
]
[\c
.BI \-o \ SSH_OPTION\c
]
[\c
.BI \-i \ IDENTITY\c
]
[\c
.BI \-J \ DESTINATION\c
]
[\c
.BI \-c \ CIPHER\c
]
[\c
.BI \-M \ HMAC\c
]
[\c
.BI \-C \ COMPRESS\c
]
[\c
.BI \-g \ CONGESTION\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
follows 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. For
example, -m 0x25 pins threads onto CPU cores 0, 2, and 5. The default
value is not specified: all CPU cores are used and no threads are
pinned to any cores.
.TP
.B \-u \fIMAX_STARTUPS\fR
Specifies the number of concurrent unauthenticated SSH connection
attempts.
.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 \-W \fICHECKPOINT\fR
Specifies a checkpoint file to save the state of a failed
transfer. When transferring fails due to, for example, connection
disruption or user interrupt,
.B mscp
writes the information about the remaining files and chunks to the
specified checkpoint file.
.B \-W
option with
.B \-D
(dry-run mode) only writes a checkpoint file and exits.
.TP
.B \-R \fICHECKPOINT\fR
Specifies a checkpoint file to resume a transfer. When a checkpoint
file is passed,
.B mscp
reads the checkpoint to load a remote host, copy direction, and files
and their chunks to be transferred. Namely,
.B mscp
can resume a past failed transfer from the checkpoint. Resuming with a
checkpoint does not require
.I source ... target
arguments. Other SSH connection options, such as port number and
config file, should be specified as with the failed run. In addition,
checkpoint files have file paths as relative paths. Thus, you must run
.B mscp
in the same working directory as the failed run. You can see the
contents of a checkpoint file with the
.B mscp \-vv \-D \-R CHECKPOINT
command (Dry-run mode). Note that the checkpoint file is not
automatically removed after the resumed transfer ends
successfully. Users should check the return value of
.B mscp
and remove the checkpoint if it returns 0.
.TP
.B \-s \fIMIN_CHUNK_SIZE\fR
Specifies the minimum chunk size.
.B mscp
divides a single file into chunks and copies the chunks in
parallel. The default value is 16M bytes.
.TP
.B \-S \fIMAX_CHUNK_SIZE\fR
Specifies the maximum chunk size. The default is file size divided by
the number of connections and devided by 4. If the calculated value
is smarller than the
.B MIN_CHUNK_SIZE
value,
MIN_CHUNK_SIZE is used.
.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 \-L \fILIMIT_BITRATE\fR
Limits the bitrate, specified with k (K), m (M), and g (G), e.g., 100m
indicates 100 Mbps.
.TP
.B \-4
Uses IPv4 addresses only.
.TP
.B \-6
Uses IPv6 addresses only.
.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,
resolves destination file paths, and exits. Dry-run mode with
.B -vv
option can confirm 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
.I scp(1).
.TP
.B \-F \fISSH_CONFIG\fR
Specifies an alternative per-user ssh configuration file. Note that
acceptable options in the configuration file are what
.I libssh
supports.
.TP
.B \-o \fISSH_OPTION\fR
Specifies ssh options in the format used in ssh_config. Note that
acceptable options are what
.I libssh
supports.
.TP
.B \-i \fIIDENTITY\fR
Specifies the identity file for public key authentication.
.TP
.B \-J \fIDESTINATION\fR
A shortcut to define a
.B ProxyJump
configuration directive. Each SFTP session of
.B mscp
connects to the target host by first making an
.B ssh
connection to the jump host described by
.I destination.
.TP
.B \-c \fICIPHER\fR
Selects the cipher to use for encrypting the data transfer. See
.B mscp -h
or
.B Ciphers
in
.UR https://\:www\:.libssh\:.org/\:features/
libssh features
.UE .
.TP
.B \-M \fIHMAC\fR
Specifies MAC hash algorithms. See
.B mscp -h
or
.B MAC hashes
in
.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 \-g \fICONGESTION\fR
Specifies the TCP congestion control algorithm to use (Linux only).
See
.B sysctl net.ipv4.tcp_allowed_congestion_control
for available values.
.TP
.B \-p
Preserves modification times and access times (file mode bits are
preserved by default).
.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
Save a checkpoint if transfer fails:
.nf
$ mscp -W mscp.checkpoint many-large-files 10.0.0.1:dst/
.fi
.PP
Check the remaining files and chunks, and resume the failed transfer:
.nf
# Dump the content of a checkpoint and exit (dry-run mode)
$ mscp -vv -D -R mscp.checkpoint
# resume transferring from the checkpoint
$ mscp -R mscp.checkpoint
.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 INFORMATION
.PP
For patches, 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>
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