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In the article "How to use SFTP to interact with a remote server" , we introduced how to connect and interact with a server using SFTP. Now let's take a look at how to perform the main operation - file transfer - after the connection is established.

Transferring files using SFTP

If we want to download a file from a remote host, we can use the get command:

sftp> get remoteFile

The download process and the output of successful download are as follows

Fetching /home/demouser/remoteFile to remoteFile
/home/demouser/remoteFile                       100%   37KB  36.8KB/s   00:

As you can see, by default, the get command downloads the remote file to a file of the same name on the local file system.

We can copy the remote file to a different name by specifying the name afterwards:

sftp> get remoteFile localFile

The get command can also be followed by some parameters. For example, we can copy a directory and all its contents by specifying the recursive option ( -r ):

sftp> get -r someDirectory

We can tell SFTP to preserve the proper permissions and access times using the -P or -p flag:

sftp> get -Pr someDirectory

Transfer local files to remote systems (upload files)

Transferring files to a remote system works the same way as downloading, but we use putthe command:

sftp> put localFile

The upload process and the output content of successful upload are as follows

Uploading localFile to /home/demouser/localFile
localFile                                     100% 7607     7.4KB/s   00:00

The options used with get also apply to put. So to copy an entire local directory, you would run put -r:

sftp> put -r localDirectory

A familiar tool that is helpful when downloading and uploading files is dfthe command, which works similarly to what it does on the command line. Using it, we can check if there is enough space to complete our transfer:

sftp> df -h

The output is as follows

Size     Used    Avail   (root)    %Capacity
  19.9GB   1016MB   17.9GB   18.9GB           4%

Note that this command cannot be used directly to view the local space, but we can use !the command.

！The command drops us into a local shell where we can run any command available on the local system. We can check our disk usage by typing:

sftp> !

Then use the following command

$ df -h

Now we can check the space of our local system.

Filesystem      Size   Used  Avail Capacity  Mounted on
/dev/disk0s2   595Gi   52Gi  544Gi     9%    /
devfs          181Ki  181Ki    0Bi   100%    /dev
map -hosts       0Bi    0Bi    0Bi   100%    /net
map auto_home    0Bi    0Bi    0Bi   100%    /home

Any other local commands will work fine. To return to our SFTP session, use the following command:

$ exit

You should now see the SFTP prompt, indicating that we are back.

Use SFTP for simple file operations

SFTP allows us to perform certain types of file system management. For example, we can change the owner of a file on the remote system using the following command:

sftp> chown userID file

Note that unlike the system chmod command, the SFTP command does not accept a username, but rather a UID. Unfortunately, there is no built-in way to learn the appropriate UID from within the SFTP interface.

As a workaround, you can /etc/passwdread from the file that associates usernames with UIDs in most Linux environments:

sftp> get /etc/passwd
sftp> !less passwd

The output is as follows

root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/bin/sh
man:x:6:12:man:/var/cache/man:/bin/sh
. . .

Note that in the second command above, instead of using the ! command on its own, we use it as a prefix to a local shell command. This will run any command available on our local machine, and can be used with the local df command as before.

The UID will be in the third column of the file and is represented by a colon character.

Likewise, we can change the group owner of a file by:

sftp> chgrp groupID file

Again, there is no built-in way to get a list of remote system groups. We can work around this with the following command:

sftp> get /etc/group
sftp> !less group

The output is as follows

root:x:0:
daemon:x:1:
bin:x:2:
sys:x:3:
adm:x:4:
tty:x:5:
disk:x:6:
lp:x:7:
. . .

The third column contains the ID of the group associated with the name in the first column. This is what we are looking for.

chmodSFTP commands work fine on remote file systems:

sftp> chmod 777 publicFile
Changing mode on /home/demouser/publicFile

There is no equivalent command for manipulating local file permissions, but you can set the local umask so that any files copied to the local system will have the appropriate permissions.

This can be lumaskdone with the command:

sftp> lumask 022
Local umask: 022

Now all regular files downloaded (as long as the -p flag is not used) will have 644 permissions.

SFTP also allows us to create directories on local and remote systems using lmkdirand respectively.mkdir

The remaining file commands target remote file systems only:

sftp> ln
sftp> rm
sftp> rmdir

These commands duplicate the core functionality of their shell equivalents. If you need to perform these operations on your local file system, remember that you can enter a shell by using the following command:

sftp> !

!Or you can execute a single command on the local system by prefixing the command like this:

sftp> !chmod 644 somefile

When you are finished with the SFTP session, use exit or bye to close the connection.

sftp> bye

Summarize

Although SFTP syntax is far less comprehensive than modern shell tools, it can be useful for providing compatibility with traditional FTP syntax or for carefully limiting the functionality available to remote users in certain environments.

For example, we can use SFTP to enable specific users to transfer files without SSH access.