neulab/tldr huggingface dataset:
--munge-links This option tells rsync to (1) modify all symlinks on the receiving side in a way that makes them unusable but recoverable (see below), or (2) to unmunge symlinks on the sending side that had been stored in a munged state.  This is useful if you don't quite trust the source of the data to not try to slip in a symlink to a unexpected place.
The way rsync disables the use of symlinks is to prefix each one with the string "/rsyncd-munged/".  This prevents the links from being used as long as that directory does not exist.  When this option is enabled, rsync will refuse to run if that path is a directory or a symlink to a directory.
The option only affects the client side of the transfer, so if you need it to affect the server, specify it via --remote-option. (Note that in a local transfer, the client side is the sender.)
This option has no affect on a daemon, since the daemon configures whether it wants munged symlinks via its "munge symlinks" parameter.  See also the "munge-symlinks" perl script in the support directory of the source code.
--copy-dirlinks, -k This option causes the sending side to treat a symlink to a directory as though it were a real directory.  This is useful if you don't want symlinks to non-directories to be affected, as they would be using --copy-links.
Without this option, if the sending side has replaced a directory with a symlink to a directory, the receiving side will delete anything that is in the way of the new symlink, including a directory hierarchy (as long as --force or --delete is in effect).
See also --keep-dirlinks for an analogous option for the receiving side.
--copy-dirlinks applies to all symlinks to directories in the source.  If you want to follow only a few specified symlinks, a trick you can use is to pass them as additional source args with a trailing slash, using --relative to make the paths match up right. For example:
rsync -r --relative src/./ src/./follow-me/ dest/
This works because rsync calls lstat(2) on the source arg as given, and the trailing slash makes lstat(2) follow the symlink, giving rise to a directory in the file-list which overrides the symlink found during the scan of "src/./".
--keep-dirlinks, -K This option causes the receiving side to treat a symlink to a directory as though it were a real directory, but only if it matches a real directory from the sender.  Without this option, the receiver's symlink would be deleted and replaced with a real directory.
For example, suppose you transfer a directory "foo" that contains a file "file", but "foo" is a symlink to directory "bar" on the receiver.  Without --keep-dirlinks, the receiver deletes symlink "foo", recreates it as a directory, and receives the file into the new directory.  With --keep-dirlinks, the receiver keeps the symlink and "file" ends up in "bar".
One note of caution: if you use --keep-dirlinks, you must trust all the symlinks in the copy! If it is possible for an untrusted user to create their own symlink to any directory, the user could then (on a subsequent copy) replace the symlink with a real directory and affect the content of whatever directory the symlink references.  For backup copies, you are better off using something like a bind mount instead of a symlink to modify your receiving hierarchy.
See also --copy-dirlinks for an analogous option for the sending side.
--hard-links, -H This tells rsync to look for hard-linked files in the source and link together the corresponding files on the destination.  Without this option, hard-linked files in the source are treated as though they were separate files.
This option does NOT necessarily ensure that the pattern of hard links on the destination exactly matches that on the source. Cases in which the destination may end up with extra hard links include the following:
o      If the destination contains extraneous hard-links (more linking than what is present in the source file list), the copying algorithm will not break them explicitly.  However, if one or more of the paths have content differences, the normal file-update process will break those extra links (unless you are using the --inplace option).
o      If you specify a --link-dest directory that contains hard links, the linking of the destination files against the --link-dest files can cause some paths in the destination to become linked together due to the --link-dest associations.
Note that rsync can only detect hard links between files that are inside the transfer set.  If rsync updates a file that has extra hard-link connections to files outside the transfer, that linkage will be broken.  If you are tempted to use the --inplace option to avoid this breakage, be very careful that you know how your files are being updated so that you are certain that no unintended changes happen due to lingering hard links (and see the --inplace option for more caveats).
If incremental recursion is active (see --recursive), rsync may transfer a missing hard-linked file before it finds that another link for that contents exists elsewhere in the hierarchy.  This does not affect the accuracy of the transfer (i.e. which files are hard-linked together), just its efficiency (i.e. copying the data for a new, early copy of a hard-linked file that could have been found later in the transfer in another member of the hard-linked set of files).  One way to avoid this inefficiency is to disable incremental recursion using the --no-inc-recursive option.
--perms, -p This option causes the receiving rsync to set the destination permissions to be the same as the source permissions. (See also the --chmod option for a way to modify what rsync considers to be the source permissions.)
When this option is off, permissions are set as follows:
o      Existing files (including updated files) retain their existing permissions, though the --executability option might change just the execute permission for the file.
o      New files get their "normal" permission bits set to the source file's permissions masked with the receiving directory's default permissions (either the receiving process's umask, or the permissions specified via the destination directory's default ACL), and their special permission bits disabled except in the case where a new directory inherits a setgid bit from its parent directory.
Thus, when --perms and --executability are both disabled, rsync's behavior is the same as that of other file-copy utilities, such as cp(1) and tar(1).
In summary: to give destination files (both old and new) the source permissions, use --perms.  To give new files the destination-default permissions (while leaving existing files unchanged), make sure that the --perms option is off and use --chmod=ugo=rwX (which ensures that all non-masked bits get enabled).  If you'd care to make this latter behavior easier to type, you could define a popt alias for it, such as putting this line in the file ~/.popt (the following defines the -Z option, and includes --no-g to use the default group of the destination dir):
rsync alias -Z --no-p --no-g --chmod=ugo=rwX
You could then use this new option in a command such as this one:
rsync -avZ src/ dest/
(Caveat: make sure that -a does not follow -Z, or it will re- enable the two --no-* options mentioned above.)
The preservation of the destination's setgid bit on newly-created directories when --perms is off was added in rsync 2.6.7.  Older rsync versions erroneously preserved the three special permission bits for newly-created files when --perms was off, while overriding the destination's setgid bit setting on a newly-created directory.  Default ACL observance was added to the ACL patch for rsync 2.6.7, so older (or non-ACL-enabled) rsyncs use the umask even if default ACLs are present.  (Keep in mind that it is the version of the receiving rsync that affects these behaviors.)
--executability, -E This option causes rsync to preserve the executability (or non- executability) of regular files when --perms is not enabled.  A regular file is considered to be executable if at least one 'x' is turned on in its permissions.  When an existing destination file's executability differs from that of the corresponding source file, rsync modifies the destination file's permissions as follows:
o      To make a file non-executable, rsync turns off all its 'x' permissions.
o      To make a file executable, rsync turns on each 'x' permission that has a corresponding 'r' permission enabled.
If --perms is enabled, this option is ignored.
--acls, -A This option causes rsync to update the destination ACLs to be the same as the source ACLs.  The option also implies --perms.
The source and destination systems must have compatible ACL entries for this option to work properly.  See the --fake-super option for a way to backup and restore ACLs that are not compatible.
--xattrs, -X This option causes rsync to update the destination extended attributes to be the same as the source ones.
For systems that support extended-attribute namespaces, a copy being done by a super-user copies all namespaces except system.*. A normal user only copies the user.* namespace.  To be able to backup and restore non-user namespaces as a normal user, see the --fake-super option.
The above name filtering can be overridden by using one or more filter options with the x modifier.  When you specify an xattr- affecting filter rule, rsync requires that you do your own system/user filtering, as well as any additional filtering for what xattr names are copied and what names are allowed to be deleted.  For example, to skip the system namespace, you could specify:
--filter='-x system.*'
To skip all namespaces except the user namespace, you could specify a negated-user match:
--filter='-x! user.*'
To prevent any attributes from being deleted, you could specify a receiver-only rule that excludes all names:
--filter='-xr *'
Note that the -X option does not copy rsync's special xattr values (e.g.  those used by --fake-super) unless you repeat the option (e.g. -XX).  This "copy all xattrs" mode cannot be used with --fake-super.
--chmod=CHMOD This option tells rsync to apply one or more comma-separated "chmod" modes to the permission of the files in the transfer.  The resulting value is treated as though it were the permissions that the sending side supplied for the file, which means that this option can seem to have no effect on existing files if --perms is not enabled.
In addition to the normal parsing rules specified in the chmod(1) manpage, you can specify an item that should only apply to a directory by prefixing it with a 'D', or specify an item that should only apply to a file by prefixing it with a 'F'.  For example, the following will ensure that all directories get marked set-gid, that no files are other-writable, that both are user- writable and group-writable, and that both have consistent executability across all bits:
--chmod=Dg+s,ug+w,Fo-w,+X
Using octal mode numbers is also allowed:
--chmod=D2775,F664
It is also legal to specify multiple --chmod options, as each additional option is just appended to the list of changes to make.
See the --perms and --executability options for how the resulting permission value can be applied to the files in the transfer.
--owner, -o This option causes rsync to set the owner of the destination file to be the same as the source file, but only if the receiving rsync is being run as the super-user (see also the --super and --fake- super options).  Without this option, the owner of new and/or transferred files are set to the invoking user on the receiving side.
The preservation of ownership will associate matching names by default, but may fall back to using the ID number in some circumstances (see also the --numeric-ids option for a full discussion).
--group, -g This option causes rsync to set the group of the destination file to be the same as the source file.  If the receiving program is not running as the super-user (or if --no-super was specified), only groups that the invoking user on the receiving side is a member of will be preserved.  Without this option, the group is set to the default group of the invoking user on the receiving side.
The preservation of group information will associate matching names by default, but may fall back to using the ID number in some circumstances (see also the --numeric-ids option for a full discussion).
--devices This option causes rsync to transfer character and block device files to the remote system to recreate these devices.  This option has no effect if the receiving rsync is not run as the super-user (see also the --super and --fake-super options).
--specials This option causes rsync to transfer special files such as named sockets and fifos.
-D     The -D option is equivalent to --devices --specials.
--write-devices This tells rsync to treat a device on the receiving side as a regular file, allowing the writing of file data into a device.
This option implies the --inplace option.
Be careful using this, as you should know what devices are present on the receiving side of the transfer, especially if running rsync as root.
This option is refused by an rsync daemon.
--times, -t This tells rsync to transfer modification times along with the files and update them on the remote system.  Note that if this option is not used, the optimization that excludes files that have not been modified cannot be effective; in other words, a missing -t or -a will cause the next transfer to behave as if it used -I, causing all files to be updated (though rsync's delta-transfer algorithm will make the update fairly efficient if the files haven't actually changed, you're much better off using -t).
--atimes, -U This tells rsync to set the access (use) times of the destination files to the same value as the source files.
If repeated, it also sets the --open-noatime option, which can help you to make the sending and receiving systems have the same access times on the transferred files without needing to run rsync an extra time after a file is transferred.
Note that some older rsync versions (prior to 3.2.0) may have been built with a pre-release --atimes patch that does not imply --open-noatime when this option is repeated.
--open-noatime This tells rsync to open files with the O_NOATIME flag (on systems that support it) to avoid changing the access time of the files that are being transferred.  If your OS does not support the O_NOATIME flag then rsync will silently ignore this option.  Note also that some filesystems are mounted to avoid updating the atime on read access even without the O_NOATIME flag being set.
--crtimes, -N, This tells rsync to set the create times (newness) of the destination files to the same value as the source files.
--omit-dir-times, -O This tells rsync to omit directories when it is preserving modification times (see --times).  If NFS is sharing the directories on the receiving side, it is a good idea to use -O. This option is inferred if you use --backup without --backup-dir.
This option also has the side-effect of avoiding early creation of directories in incremental recursion copies.  The default --inc- recursive copying normally does an early-create pass of all the sub-directories in a parent directory in order for it to be able to then set the modify time of the parent directory right away (without having to delay that until a bunch of recursive copying has finished).  This early-create idiom is not necessary if directory modify times are not being preserved, so it is skipped. Since early-create directories don't have accurate mode, mtime, or ownership, the use of this option can help when someone wants to avoid these partially-finished directories.
--omit-link-times, -J This tells rsync to omit symlinks when it is preserving modification times (see --times).
--super This tells the receiving side to attempt super-user activities even if the receiving rsync wasn't run by the super-user.  These activities include: preserving users via the --owner option, preserving all groups (not just the current user's groups) via the --groups option, and copying devices via the --devices option. This is useful for systems that allow such activities without being the super-user, and also for ensuring that you will get errors if the receiving side isn't being run as the super-user. To turn off super-user activities, the super-user can use --no- super.
--fake-super When this option is enabled, rsync simulates super-user activities by saving/restoring the privileged attributes via special extended attributes that are attached to each file (as needed).  This includes the file's owner and group (if it is not the default), the file's device info (device & special files are created as empty text files), and any permission bits that we won't allow to be set on the real file (e.g. the real file gets u-s,g-s,o-t for safety) or that would limit the owner's access (since the real super-user can always access/change a file, the files we create can always be accessed/changed by the creating user).  This option also handles ACLs (if --acls was specified) and non-user extended attributes (if --xattrs was specified).
This is a good way to backup data without using a super-user, and to store ACLs from incompatible systems.
The --fake-super option only affects the side where the option is used.  To affect the remote side of a remote-shell connection, use the --remote-option (-M) option:
rsync -av -M--fake-super /src/ host:/dest/
For a local copy, this option affects both the source and the destination.  If you wish a local copy to enable this option just for the destination files, specify -M--fake-super.  If you wish a local copy to enable this option just for the source files, combine --fake-super with -M--super.
This option is overridden by both --super and --no-super.
See also the "fake super" setting in the daemon's rsyncd.conf file.
--sparse, -S Try to handle sparse files efficiently so they take up less space on the destination.  If combined with --inplace the file created might not end up with sparse blocks with some combinations of kernel version and/or filesystem type.  If --whole-file is in effect (e.g. for a local copy) then it will always work because rsync truncates the file prior to writing out the updated version.
Note that versions of rsync older than 3.1.3 will reject the combination of --sparse and --inplace.
--preallocate This tells the receiver to allocate each destination file to its eventual size before writing data to the file.  Rsync will only use the real filesystem-level preallocation support provided by Linux's fallocate(2) system call or Cygwin's posix_fallocate(3), not the slow glibc implementation that writes a null byte into each block.
Without this option, larger files may not be entirely contiguous on the filesystem, but with this option rsync will probably copy more slowly.  If the destination is not an extent-supporting filesystem (such as ext4, xfs, NTFS, etc.), this option may have no positive effect at all.
If combined with --sparse, the file will only have sparse blocks (as opposed to allocated sequences of null bytes) if the kernel version and filesystem type support creating holes in the allocated data.
--dry-run, -n This makes rsync perform a trial run that doesn't make any changes (and produces mostly the same output as a real run).  It is most commonly used in combination with the --verbose, -v and/or --itemize-changes, -i options to see what an rsync command is going to do before one actually runs it.
The output of --itemize-changes is supposed to be exactly the same on a dry run and a subsequent real run (barring intentional trickery and system call failures); if it isn't, that's a bug. Other output should be mostly unchanged, but may differ in some areas.  Notably, a dry run does not send the actual data for file transfers, so --progress has no effect, the "bytes sent", "bytes received", "literal data", and "matched data" statistics are too small, and the "speedup" value is equivalent to a run where no file transfers were needed.
--whole-file, -W This option disables rsync's delta-transfer algorithm, which causes all transferred files to be sent whole.  The transfer may be faster if this option is used when the bandwidth between the source and destination machines is higher than the bandwidth to disk (especially when the "disk" is actually a networked filesystem).  This is the default when both the source and destination are specified as local paths, but only if no batch- writing option is in effect.
--checksum-choice=STR, --cc=STR This option overrides the checksum algorithms.  If one algorithm name is specified, it is used for both the transfer checksums and (assuming --checksum is specified) the pre-transfer checksums.  If two comma-separated names are supplied, the first name affects the transfer checksums, and the second name affects the pre-transfer checksums (-c).
The checksum options that you may be able to use are:
o      auto (the default automatic choice)
o      xxh128
o      xxh3
o      xxh64 (aka xxhash)
o      md5
o      md4
o      none
Run rsync --version to see the default checksum list compiled into your version (which may differ from the list above).
If "none" is specified for the first (or only) name, the --whole- file option is forced on and no checksum verification is performed on the transferred data.  If "none" is specified for the second (or only) name, the --checksum option cannot be used.
The "auto" option is the default, where rsync bases its algorithm choice on a negotiation between the client and the server as follows:
When both sides of the transfer are at least 3.2.0, rsync chooses the first algorithm in the client's list of choices that is also in the server's list of choices.  If no common checksum choice is found, rsync exits with an error.  If the remote rsync is too old to support checksum negotiation, a value is chosen based on the protocol version (which chooses between MD5 and various flavors of MD4 based on protocol age).
The default order can be customized by setting the environment variable RSYNC_CHECKSUM_LIST to a space-separated list of acceptable checksum names.  If the string contains a "&" character, it is separated into the "client string & server string", otherwise the same string applies to both.  If the string (or string portion) contains no non-whitespace characters, the default checksum list is used.  This method does not allow you to specify the transfer checksum separately from the pre-transfer checksum, and it discards "auto" and all unknown checksum names. A list with only invalid names results in a failed negotiation.
The use of the --checksum-choice option overrides this environment list.
--one-file-system, -x This tells rsync to avoid crossing a filesystem boundary when recursing.  This does not limit the user's ability to specify items to copy from multiple filesystems, just rsync's recursion through the hierarchy of each directory that the user specified, and also the analogous recursion on the receiving side during deletion.  Also keep in mind that rsync treats a "bind" mount to the same device as being on the same filesystem.
If this option is repeated, rsync omits all mount-point directories from the copy.  Otherwise, it includes an empty directory at each mount-point it encounters (using the attributes of the mounted directory because those of the underlying mount- point directory are inaccessible).
If rsync has been told to collapse symlinks (via --copy-links or --copy-unsafe-links), a symlink to a directory on another device is treated like a mount-point.  Symlinks to non-directories are unaffected by this option.
--existing, --ignore-non-existing This tells rsync to skip creating files (including directories) that do not exist yet on the destination.  If this option is combined with the --ignore-existing option, no files will be updated (which can be useful if all you want to do is delete extraneous files).
--ignore-existing This tells rsync to skip updating files that already exist on the destination (this does not ignore existing directories, or nothing would get done).  See also --existing.
This option can be useful for those doing backups using the --link-dest option when they need to continue a backup run that got interrupted.  Since a --link-dest run is copied into a new directory hierarchy (when it is used properly), using --ignore- existing will ensure that the already-handled files don't get tweaked (which avoids a change in permissions on the hard-linked files).  This does mean that this option is only looking at the existing files in the destination hierarchy itself.
--remove-source-files This tells rsync to remove from the sending side the files (meaning non-directories) that are a part of the transfer and have been successfully duplicated on the receiving side.
Note that you should only use this option on source files that are quiescent.  If you are using this to move files that show up in a particular directory over to another host, make sure that the finished files get renamed into the source directory, not directly written into it, so that rsync can't possibly transfer a file that is not yet fully written.  If you can't first write the files into a different directory, you should use a naming idiom that lets rsync avoid transferring files that are not yet finished (e.g. name the file "foo.new" when it is written, rename it to "foo" when it is done, and then use the option --exclude='*.new' for the rsync transfer).
Starting with 3.1.0, rsync will skip the sender-side removal (and output an error) if the file's size or modify time has not stayed unchanged.
--delete This tells rsync to delete extraneous files from the receiving side (ones that aren't on the sending side), but only for the directories that are being synchronized.  You must have asked rsync to send the whole directory (e.g. "dir" or "dir/") without using a wildcard for the directory's contents (e.g. "dir/*") since the wildcard is expanded by the shell and rsync thus gets a request to transfer individual files, not the files' parent directory.  Files that are excluded from the transfer are also excluded from being deleted unless you use the --delete-excluded option or mark the rules as only matching on the sending side (see the include/exclude modifiers in the FILTER RULES section).
Prior to rsync 2.6.7, this option would have no effect unless --recursive was enabled.  Beginning with 2.6.7, deletions will also occur when --dirs (-d) is enabled, but only for directories whose contents are being copied.
This option can be dangerous if used incorrectly! It is a very good idea to first try a run using the --dry-run option (-n) to see what files are going to be deleted.
If the sending side detects any I/O errors, then the deletion of any files at the destination will be automatically disabled.  This is to prevent temporary filesystem failures (such as NFS errors) on the sending side from causing a massive deletion of files on the destination.  You can override this with the --ignore-errors option.
The --delete option may be combined with one of the --delete-WHEN options without conflict, as well as --delete-excluded.  However, if none of the --delete-WHEN options are specified, rsync will choose the --delete-during algorithm when talking to rsync 3.0.0 or newer, and the --delete-before algorithm when talking to an older rsync.  See also --delete-delay and --delete-after.
--delete-before Request that the file-deletions on the receiving side be done before the transfer starts.  See --delete (which is implied) for more details on file-deletion.
Deleting before the transfer is helpful if the filesystem is tight for space and removing extraneous files would help to make the transfer possible.  However, it does introduce a delay before the start of the transfer, and this delay might cause the transfer to timeout (if --timeout was specified).  It also forces rsync to use the old, non-incremental recursion algorithm that requires rsync to scan all the files in the transfer into memory at once (see --recursive).
--delete-during, --del Request that the file-deletions on the receiving side be done incrementally as the transfer happens.  The per-directory delete scan is done right before each directory is checked for updates, so it behaves like a more efficient --delete-before, including doing the deletions prior to any per-directory filter files being updated.  This option was first added in rsync version 2.6.4.  See --delete (which is implied) for more details on file-deletion.
--delete-delay Request that the file-deletions on the receiving side be computed during the transfer (like --delete-during), and then removed after the transfer completes.  This is useful when combined with --delay-updates and/or --fuzzy, and is more efficient than using --delete-after (but can behave differently, since --delete-after computes the deletions in a separate pass after all updates are done).  If the number of removed files overflows an internal buffer, a temporary file will be created on the receiving side to hold the names (it is removed while open, so you shouldn't see it during the transfer).  If the creation of the temporary file fails, rsync will try to fall back to using --delete-after (which it cannot do if --recursive is doing an incremental scan).  See --delete (which is implied) for more details on file-deletion.
--delete-after Request that the file-deletions on the receiving side be done after the transfer has completed.  This is useful if you are sending new per-directory merge files as a part of the transfer and you want their exclusions to take effect for the delete phase of the current transfer.  It also forces rsync to use the old, non-incremental recursion algorithm that requires rsync to scan all the files in the transfer into memory at once (see --recursive). See --delete (which is implied) for more details on file-deletion.
--delete-excluded In addition to deleting the files on the receiving side that are not on the sending side, this tells rsync to also delete any files on the receiving side that are excluded (see --exclude).  See the FILTER RULES section for a way to make individual exclusions behave this way on the receiver, and for a way to protect files from --delete-excluded.  See --delete (which is implied) for more details on file-deletion.
--ignore-missing-args When rsync is first processing the explicitly requested source files (e.g.  command-line arguments or --files-from entries), it is normally an error if the file cannot be found.  This option suppresses that error, and does not try to transfer the file. This does not affect subsequent vanished-file errors if a file was initially found to be present and later is no longer there.
--delete-missing-args This option takes the behavior of (the implied) --ignore-missing- args option a step farther: each missing arg will become a deletion request of the corresponding destination file on the receiving side (should it exist).  If the destination file is a non-empty directory, it will only be successfully deleted if --force or --delete are in effect.  Other than that, this option is independent of any other type of delete processing.
The missing source files are represented by special file-list entries which display as a "*missing" entry in the --list-only output.
--ignore-errors Tells --delete to go ahead and delete files even when there are I/O errors.
--force This option tells rsync to delete a non-empty directory when it is to be replaced by a non-directory.  This is only relevant if deletions are not active (see --delete for details).
Note for older rsync versions: --force used to still be required when using --delete-after, and it used to be non-functional unless the --recursive option was also enabled.
--max-delete=NUM This tells rsync not to delete more than NUM files or directories. If that limit is exceeded, all further deletions are skipped through the end of the transfer.  At the end, rsync outputs a warning (including a count of the skipped deletions) and exits with an error code of 25 (unless some more important error condition also occurred).
Beginning with version 3.0.0, you may specify --max-delete=0 to be warned about any extraneous files in the destination without removing any of them.  Older clients interpreted this as "unlimited", so if you don't know what version the client is, you can use the less obvious --max-delete=-1 as a backward-compatible way to specify that no deletions be allowed (though really old versions didn't warn when the limit was exceeded).
--max-size=SIZE This tells rsync to avoid transferring any file that is larger than the specified SIZE.  A numeric value can be suffixed with a string to indicate the numeric units or left unqualified to specify bytes.  Feel free to use a fractional value along with the units, such as --max-size=1.5m.
The first letter of a units string can be B (bytes), K (kilo), M (mega), G (giga), T (tera), or P (peta).  If the string is a single char or has "ib" added to it (e.g. "G" or "GiB") then the units are multiples of 1024.  If you use a two-letter suffix that ends with a "B" (e.g. "kb") then you get units that are multiples of 1000.  The string's letters can be any mix of upper and lower- case that you want to use.
Finally, if the string ends with either "+1" or "-1", it is offset by one byte in the indicated direction.  The largest possible value is usually 8192P-1.
Examples: --max-size=1.5mb-1 is 1499999 bytes, and --max-size=2g+1 is 2147483649 bytes.
Note that rsync versions prior to 3.1.0 did not allow --max- size=0.
--min-size=SIZE This tells rsync to avoid transferring any file that is smaller than the specified SIZE, which can help in not transferring small, junk files.  See the --max-size option for a description of SIZE and other information.
Note that rsync versions prior to 3.1.0 did not allow --min- size=0.
--max-alloc=SIZE By default rsync limits an individual malloc/realloc to about 1GB in size.  For most people this limit works just fine and prevents a protocol error causing rsync to request massive amounts of memory.  However, if you have many millions of files in a transfer, a large amount of server memory, and you don't want to split up your transfer into multiple parts, you can increase the per-allocation limit to something larger and rsync will consume more memory.
Keep in mind that this is not a limit on the total size of allocated memory.  It is a sanity-check value for each individual allocation.
See the --max-size option for a description of how SIZE can be specified.  The default suffix if none is given is bytes.
Beginning in 3.2.3, a value of 0 specifies no limit.
You can set a default value using the environment variable RSYNC_MAX_ALLOC using the same SIZE values as supported by this option.  If the remote rsync doesn't understand the --max-alloc option, you can override an environmental value by specifying --max-alloc=1g, which will make rsync avoid sending the option to the remote side (because "1G" is the default).
--block-size=SIZE, -B This forces the block size used in rsync's delta-transfer algorithm to a fixed value.  It is normally selected based on the size of each file being updated.  See the technical report for details.
Beginning in 3.2.3 the SIZE can be specified with a suffix as detailed in the --max-size option.  Older versions only accepted a byte count.
--rsh=COMMAND, -e This option allows you to choose an alternative remote shell program to use for communication between the local and remote copies of rsync.  Typically, rsync is configured to use ssh by default, but you may prefer to use rsh on a local network.
If this option is used with [user@]host::module/path, then the remote shell COMMAND will be used to run an rsync daemon on the remote host, and all data will be transmitted through that remote shell connection, rather than through a direct socket connection to a running rsync daemon on the remote host.  See the section "USING RSYNC-DAEMON FEATURES VIA A REMOTE-SHELL CONNECTION" above.
Beginning with rsync 3.2.0, the RSYNC_PORT environment variable will be set when a daemon connection is being made via a remote- shell connection.  It is set to 0 if the default daemon port is being assumed, or it is set to the value of the rsync port that was specified via either the --port option or a non-empty port value in an rsync:// URL.  This allows the script to discern if a non-default port is being requested, allowing for things such as an SSL or stunnel helper script to connect to a default or alternate port.
Command-line arguments are permitted in COMMAND provided that COMMAND is presented to rsync as a single argument.  You must use spaces (not tabs or other whitespace) to separate the command and args from each other, and you can use single- and/or double-quotes to preserve spaces in an argument (but not backslashes).  Note that doubling a single-quote inside a single-quoted string gives you a single-quote; likewise for double-quotes (though you need to pay attention to which quotes your shell is parsing and which quotes rsync is parsing).  Some examples:
-e 'ssh -p 2234' -e 'ssh -o "ProxyCommand nohup ssh firewall nc -w1 %h %p"'
(Note that ssh users can alternately customize site-specific connect options in their .ssh/config file.)
You can also choose the remote shell program using the RSYNC_RSH environment variable, which accepts the same range of values as -e.
See also the --blocking-io option which is affected by this option.
--rsync-path=PROGRAM Use this to specify what program is to be run on the remote machine to start-up rsync.  Often used when rsync is not in the default remote-shell's path (e.g. --rsync- path=/usr/local/bin/rsync).  Note that PROGRAM is run with the help of a shell, so it can be any program, script, or command sequence you'd care to run, so long as it does not corrupt the standard-in & standard-out that rsync is using to communicate.
One tricky example is to set a different default directory on the remote machine for use with the --relative option.  For instance:
rsync -avR --rsync-path="cd /a/b && rsync" host:c/d /e/
--remote-option=OPTION, -M This option is used for more advanced situations where you want certain effects to be limited to one side of the transfer only. For instance, if you want to pass --log-file=FILE and --fake-super to the remote system, specify it like this:
rsync -av -M --log-file=foo -M--fake-super src/ dest/
If you want to have an option affect only the local side of a transfer when it normally affects both sides, send its negation to the remote side.  Like this:
rsync -av -x -M--no-x src/ dest/
Be cautious using this, as it is possible to toggle an option that will cause rsync to have a different idea about what data to expect next over the socket, and that will make it fail in a cryptic fashion.
Note that it is best to use a separate --remote-option for each option you want to pass.  This makes your usage compatible with the --protect-args option.  If that option is off, any spaces in your remote options will be split by the remote shell unless you take steps to protect them.
When performing a local transfer, the "local" side is the sender and the "remote" side is the receiver.
Note some versions of the popt option-parsing library have a bug in them that prevents you from using an adjacent arg with an equal in it next to a short option letter (e.g. -M--log-file=/tmp/foo). If this bug affects your version of popt, you can use the version of popt that is included with rsync.
--cvs-exclude, -C This is a useful shorthand for excluding a broad range of files that you often don't want to transfer between systems.  It uses a similar algorithm to CVS to determine if a file should be ignored.
The exclude list is initialized to exclude the following items (these initial items are marked as perishable -- see the FILTER RULES section):
RCS SCCS CVS CVS.adm RCSLOG cvslog.*  tags TAGS .make.state .nse_depinfo *~ #* .#* ,* _$* *$ *.old *.bak *.BAK *.orig *.rej .del-* *.a *.olb *.o *.obj *.so *.exe *.Z *.elc *.ln core .svn/ .git/ .hg/ .bzr/
then, files listed in a $HOME/.cvsignore are added to the list and any files listed in the CVSIGNORE environment variable (all cvsignore names are delimited by whitespace).
Finally, any file is ignored if it is in the same directory as a .cvsignore file and matches one of the patterns listed therein. Unlike rsync's filter/exclude files, these patterns are split on whitespace.  See the cvs(1) manual for more information.
If you're combining -C with your own --filter rules, you should note that these CVS excludes are appended at the end of your own rules, regardless of where the -C was placed on the command-line. This makes them a lower priority than any rules you specified explicitly.  If you want to control where these CVS excludes get inserted into your filter rules, you should omit the -C as a command-line option and use a combination of --filter=:C and --filter=-C (either on your command-line or by putting the ":C" and "-C" rules into a filter file with your other rules).  The first option turns on the per-directory scanning for the .cvsignore file.  The second option does a one-time import of the CVS excludes mentioned above.
--filter=RULE, -f This option allows you to add rules to selectively exclude certain files from the list of files to be transferred.  This is most useful in combination with a recursive transfer.
You may use as many --filter options on the command line as you like to build up the list of files to exclude.  If the filter contains whitespace, be sure to quote it so that the shell gives the rule to rsync as a single argument.  The text below also mentions that you can use an underscore to replace the space that separates a rule from its arg.
See the FILTER RULES section for detailed information on this option.
-F     The -F option is a shorthand for adding two --filter rules to your command.  The first time it is used is a shorthand for this rule:
--filter='dir-merge /.rsync-filter'
This tells rsync to look for per-directory .rsync-filter files that have been sprinkled through the hierarchy and use their rules to filter the files in the transfer.  If -F is repeated, it is a shorthand for this rule:
--filter='exclude .rsync-filter'
This filters out the .rsync-filter files themselves from the transfer.
See the FILTER RULES section for detailed information on how these options work.
--exclude=PATTERN This option is a simplified form of the --filter option that defaults to an exclude rule and does not allow the full rule- parsing syntax of normal filter rules.
--exclude-from=FILE This option is related to the --exclude option, but it specifies a FILE that contains exclude patterns (one per line).  Blank lines in the file and lines starting with ';' or '#' are ignored.  If FILE is '-', the list will be read from standard input.
--include=PATTERN This option is a simplified form of the --filter option that defaults to an include rule and does not allow the full rule- parsing syntax of normal filter rules.
--include-from=FILE This option is related to the --include option, but it specifies a FILE that contains include patterns (one per line).  Blank lines in the file and lines starting with ';' or '#' are ignored.  If FILE is '-', the list will be read from standard input.
--files-from=FILE Using this option allows you to specify the exact list of files to transfer (as read from the specified FILE or '-' for standard input).  It also tweaks the default behavior of rsync to make transferring just the specified files and directories easier:
o      The --relative (-R) option is implied, which preserves the path information that is specified for each item in the file (use --no-relative or --no-R if you want to turn that off).
o      The --dirs (-d) option is implied, which will create directories specified in the list on the destination rather than noisily skipping them (use --no-dirs or --no-d if you want to turn that off).
o      The --archive (-a) option's behavior does not imply --recursive (-r), so specify it explicitly, if you want it.
o      These side-effects change the default state of rsync, so the position of the --files-from option on the command-line has no bearing on how other options are parsed (e.g. -a works the same before or after --files-from, as does --no-R and all other options).
The filenames that are read from the FILE are all relative to the source dir -- any leading slashes are removed and no ".." references are allowed to go higher than the source dir.  For example, take this command:
rsync -a --files-from=/tmp/foo /usr remote:/backup
If /tmp/foo contains the string "bin" (or even "/bin"), the /usr/bin directory will be created as /backup/bin on the remote host.  If it contains "bin/" (note the trailing slash), the immediate contents of the directory would also be sent (without needing to be explicitly mentioned in the file -- this began in version 2.6.4).  In both cases, if the -r option was enabled, that dir's entire hierarchy would also be transferred (keep in mind that -r needs to be specified explicitly with --files-from, since it is not implied by -a).  Also note that the effect of the (enabled by default) --relative option is to duplicate only the path info that is read from the file -- it does not force the duplication of the source-spec path (/usr in this case).
In addition, the --files-from file can be read from the remote host instead of the local host if you specify a "host:" in front of the file (the host must match one end of the transfer).  As a short-cut, you can specify just a prefix of ":" to mean "use the remote end of the transfer".  For example:
rsync -a --files-from=:/path/file-list src:/ /tmp/copy
This would copy all the files specified in the /path/file-list file that was located on the remote "src" host.
If the --iconv and --protect-args options are specified and the --files-from filenames are being sent from one host to another, the filenames will be translated from the sending host's charset to the receiving host's charset.
NOTE: sorting the list of files in the --files-from input helps rsync to be more efficient, as it will avoid re-visiting the path elements that are shared between adjacent entries.  If the input is not sorted, some path elements (implied directories) may end up being scanned multiple times, and rsync will eventually unduplicate them after they get turned into file-list elements.
--from0, -0 This tells rsync that the rules/filenames it reads from a file are terminated by a null ('\0') character, not a NL, CR, or CR+LF. This affects --exclude-from, --include-from, --files-from, and any merged files specified in a --filter rule.  It does not affect --cvs-exclude (since all names read from a .cvsignore file are split on whitespace).
--protect-args, -s This option sends all filenames and most options to the remote rsync without allowing the remote shell to interpret them.  This means that spaces are not split in names, and any non-wildcard special characters are not translated (such as ~, $, ;, &, etc.). Wildcards are expanded on the remote host by rsync (instead of the shell doing it).
If you use this option with --iconv, the args related to the remote side will also be translated from the local to the remote character-set.  The translation happens before wild-cards are expanded.  See also the --files-from option.
You may also control this option via the RSYNC_PROTECT_ARGS environment variable.  If this variable has a non-zero value, this option will be enabled by default, otherwise it will be disabled by default.  Either state is overridden by a manually specified positive or negative version of this option (note that --no-s and --no-protect-args are the negative versions).  Since this option was first introduced in 3.0.0, you'll need to make sure it's disabled if you ever need to interact with a remote rsync that is older than that.
Rsync can also be configured (at build time) to have this option enabled by default (with is overridden by both the environment and the command-line).  Run rsync --version to check if this is the case, as it will display "default protect-args" or "optional protect-args" depending on how it was compiled.
This option will eventually become a new default setting at some as-yet-undetermined point in the future.
--copy-as=USER[:GROUP] This option instructs rsync to use the USER and (if specified after a colon) the GROUP for the copy operations.  This only works if the user that is running rsync has the ability to change users. If the group is not specified then the user's default groups are used.