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Use scp when you need to copy files between an Ubuntu computer and a reachable SSH server. Install the OpenSSH client, authenticate to the remote account, and run scp source target. A remote location uses the form [user@]host:path; putting the remote location first downloads a file, while putting it second uploads one.
On current OpenSSH releases, including Ubuntu installations using OpenSSH 9.0 or newer, scp uses the SFTP protocol by default. The legacy SCP/rcp protocol remains available with -O for compatibility, but it should not be your routine setting. This guide shows the exact commands, key authentication, directory transfers, port and identity options, protocol differences, and safe troubleshooting.
What SCP on Ubuntu does
scp is the OpenSSH secure file-copy command. It transfers data through an SSH connection, so the remote computer must run an SSH server, accept connections from your Ubuntu machine, and authenticate your account. Ubuntu’s documentation describes the server daemon, sshd, as handling those client connections; the file transfer begins after authentication. Network reachability, firewall rules, the listening port, and the server’s account permissions still determine whether a transfer can work.
The command itself is included in the OpenSSH client software. It is not a separate commercial product and does not require a special hardware accessory.
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Install the required OpenSSH packages
Install the client on the Ubuntu computer that runs SCP
Open a terminal and install the client package:
sudo apt install openssh-clientYou need this package on the machine from which you type the scp command. If it is already installed, APT reports that the newest version is present.
Install the server on an Ubuntu destination
An Ubuntu computer that must accept incoming transfers needs the server package:
sudo apt install openssh-serverThe remote host also needs a reachable SSH service and an account that can log in. Installation alone does not guarantee reachability: a firewall, cloud security rule, routing problem, stopped service, or nonstandard port can still block the connection. Canonical’s OpenSSH server documentation covers server setup and administration.
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Understand SCP’s source-and-target syntax
The general form is:
scp [options] source targetA remote source or target is written as:
[user@]host:pathThe endpoint without a host name is local. Therefore, direction is determined by position:
| Task | Command shape | What happens |
|---|---|---|
| Upload from Ubuntu to a server | scp local-file user@host:/remote/path/ |
The local file is the source; the remote path is the destination. |
| Download from a server to Ubuntu | scp user@host:/remote/file /local/path/ |
The remote file is the source; the local path is the destination. |
Use an absolute remote path when you want an unambiguous destination, such as /home/alice/. A path ending in / indicates a directory. If the destination directory does not exist or your account cannot write there, the transfer fails after connection and authentication.
If a local filename contains a colon, use an explicit relative or absolute path so scp does not mistake the colon for the separator in a host specification. For example, use ./notes:2026.txt rather than passing an ambiguous bare name.
Copy a single file
Upload a local file
This example sends report.txt from the current Ubuntu directory to Alice’s home directory on example.net:
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scp report.txt alice@example.net:/home/alice/You will be prompted for Alice’s SSH password unless another authentication method, such as a key, is already configured. The destination file normally keeps the source filename, so this creates /home/alice/report.txt.
Download a remote file
Place the remote specification first to retrieve a file into the current local directory:
scp alice@example.net:/home/alice/report.txt .The dot means “the current local directory.” You can instead choose a directory or a new filename, for example:
scp alice@example.net:/home/alice/report.txt ~/Downloads/report-copy.txtCopy to a different remote filename
A destination path can include a new basename:
scp report.txt alice@example.net:/home/alice/archive/report-2026.txtThe remote account must be able to create or replace that file in the target directory. SCP does not elevate privileges on the server; a normal account cannot write to protected directories unless the server-side permissions or workflow explicitly allow it.
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Add uppercase -r when the source is a directory:
scp -r project/ alice@example.net:/home/alice/This copies the directory and its contents below the remote home directory. To download a remote directory into the current local directory, reverse the endpoints:
scp -r alice@example.net:/home/alice/project/ .Check the resulting path before starting a large transfer. A destination such as /home/alice/backup/ can result in /home/alice/backup/project/, while a destination naming an existing directory may place the source directory inside it. The Ubuntu Noble scp manual documents recursive copying and the complete option set.
Use a nonstandard SSH port or a specific key
Connect to a different port with uppercase -P
SSH servers commonly listen on port 22, but an administrator may configure another port. Use uppercase -P:
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scp -P 2222 report.txt alice@example.net:/home/alice/Option capitalization matters. Lowercase -p does something else: it asks scp to preserve modification times, access times, and file modes from the source. It does not select a port.
Select an identity file with -i
If the account requires a particular private key, specify it with -i:
scp -i ~/.ssh/id_ed25519 report.txt alice@example.net:/home/alice/The private key must be readable by your local user and should be protected from other users. If the key has a passphrase, SSH asks for it when needed. You can avoid repeating the full option by defining a host alias and identity in ~/.ssh/config; Ubuntu’s OpenSSH guidance discusses host-specific key configuration.
Set up SSH-key authentication
Keys are useful when you transfer regularly or need noninteractive authentication. The private key stays on the Ubuntu client; the corresponding public key is placed in the remote account’s authorized keys. A passphrase protects the private key if the client filesystem is exposed.
- Create an Ed25519 key pair. Run:
ssh-keygen -t ed25519Accept the suggested location or enter another one, and choose a passphrase when prompted. The private key is normally stored under
~/.ssh; do not copy it to the server. - Install the public key on the remote account. Run:
ssh-copy-id alice@example.netThe command asks for the account’s current password and appends the public key to the remote account’s authorized-key file.
- Test SSH before testing SCP. Run:
ssh alice@example.netIf an interactive SSH login fails, fix the host, port, account, key, or server configuration before diagnosing the file copy.
- Use the key for the transfer if necessary.
scp -i ~/.ssh/id_ed25519 report.txt alice@example.net:/home/alice/
For a server using a custom port, include the same port in both the SSH test and the SCP command, for example ssh -p 2222 alice@example.net and scp -P 2222 .... SSH uses lowercase -p for its port option, whereas SCP uses uppercase -P; do not transfer the capitalization between commands.
Know which SCP protocol your client is using
OpenSSH 9.0, released on 2022-04-08, changed the default implementation: its release notes state, “This release switches scp(1) from using the legacy scp/rcp protocol to using the SFTP protocol by default.” Modern clients therefore retain the scp command interface while using SFTP for the transfer operation. Read the OpenSSH 9.0 release notes for the change announcement.
| Mode | How to select it | Important behavior | When it matters |
|---|---|---|---|
| Modern SFTP-backed mode | Default on OpenSSH 9.0 and newer | Uses SFTP semantics rather than remote-shell wildcard expansion. | Use this for ordinary transfers when the server supports the required SFTP behavior. |
| Legacy SCP/rcp mode | Add -O |
Uses the older protocol and expands remote wildcards through the remote shell. | Compatibility with an older server or appliance that cannot handle the client’s SFTP-based operation. |
Do not treat -O as a performance switch or a routine fix. It changes protocol behavior. In legacy mode, shell metacharacters and wildcards require careful quoting because expansion occurs on the remote shell. For example, a pattern intended for the remote host must be quoted so your local shell does not expand it first:
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scp -O 'alice@example.net:/home/alice/logs/*.gz' .Exact wildcard behavior can vary with the remote shell and filenames. If a current client reports an SFTP-related protocol error, verify the actual server or appliance implementation before selecting legacy mode. The Noble manual documents current behavior, while the Ubuntu Jammy manual describes an older package generation whose default behavior may differ. SFTP support is not universal across every SSH server or embedded appliance.
Choose password or key authentication
| Authentication method | Best fit | Advantages | Things to manage |
|---|---|---|---|
| Password | Occasional, interactive copies | No key setup; works when the server permits password login. | Requires a prompt for each connection and depends on the server’s password policy. |
| Ed25519 SSH key | Frequent transfers, scripts, or multiple hosts | Can avoid repeated account-password entry and can be selected per host. | Protect the private key, use a passphrase, and keep the public key correctly installed on the remote account. |
Authentication does not grant extra filesystem rights. After login, the remote account still needs read permission for a download, write permission for an upload, and directory traversal permission for every parent directory in the path.
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Work from the endpoint and authentication basics toward server diagnostics. Avoid changing security settings blindly.
1. Confirm the host, account, and path
- Check the spelling of the host name and username.
- Confirm that the remote path exists and is written for the remote operating system.
- For a download, verify that the account can read the source file.
- For an upload, verify that the destination directory exists and is writable.
- Confirm whether the server uses port 22 or a custom port, and pass the correct value with uppercase
-P.
2. Test the SSH connection separately
Run SSH with the same account and port before repeating the copy:
ssh -p 2222 alice@example.netOmit -p 2222 when the server uses the default port. If SSH cannot establish a session, SCP cannot transfer the file. Resolve DNS, routing, firewall, service availability, or authentication first.
3. Turn on SCP’s verbose diagnostics
Add -v to see client-side connection, host-key, authentication, and transfer details:
scp -v report.txt alice@example.net:/home/alice/For a custom port or key, keep those options in the diagnostic command:
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scp -v -P 2222 -i ~/.ssh/id_ed25519 report.txt alice@example.net:/home/alice/A successful command returns status 0. A nonzero status indicates an error; the verbose output usually identifies the stage at which it occurred.
4. Inspect the remote SSH service when you administer it
On an Ubuntu server you control, follow the SSH service log while reproducing the failure:
sudo journalctl -fu ssh.serviceLook for rejected users, invalid keys, denied authentication methods, connection limits, or subsystem errors. If you edit the server configuration, validate it before restarting:
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sudo sshd -tOnly restart after the syntax check succeeds. A malformed configuration can lock administrators out. This server-side check is not a routine step on the client that merely runs scp.
5. Treat host-key warnings as security events
If SSH reports that a host key changed, do not disable host-key checking as a casual workaround. A legitimate server rebuild or key rotation is possible, but an unexpected change can indicate that you are connecting to the wrong host or that the connection is being intercepted. Verify the new fingerprint with the server owner or administrator, then update the local known-host entry through an approved process.
6. Investigate protocol compatibility
If authentication succeeds but the transfer fails with a subsystem or protocol complaint, determine the client OpenSSH version and the remote server’s SFTP support. On a modern client, try the normal command first. Use -O only when the administrator confirms that legacy SCP/rcp is required by that server. Do not assume that every device advertising SSH implements SFTP identically.
Security practices for routine SCP use
- Verify the destination. A valid SSH login does not prove that the host is the intended system; confirm host keys and use a known hostname or verified address.
- Prefer key authentication with a passphrase for recurring work, while keeping the private key on the client and restricting access to it.
- Limit the remote account. Use an account with only the filesystem access required for the transfer rather than an administrator account.
- Quote carefully. Spaces and shell metacharacters can be interpreted by a local shell, and legacy
-Omode adds remote-shell expansion concerns. Quote paths deliberately and test unusual names with a small transfer. - Check permissions before using elevated access. SCP does not run a remote command through
sudoto write protected files. Transfer to an account-owned directory, then use an approved server-side move procedure if necessary. - Do not expose secrets in shell history. SCP reads passwords interactively; never put a password directly into the command line.
Practical command reference
| Purpose | Command |
|---|---|
| Install client | sudo apt install openssh-client |
| Install Ubuntu server | sudo apt install openssh-server |
| Upload one file | scp report.txt alice@example.net:/home/alice/ |
| Download one file | scp alice@example.net:/home/alice/report.txt . |
| Upload a directory | scp -r project/ alice@example.net:/home/alice/ |
| Use port 2222 | scp -P 2222 report.txt alice@example.net:/home/alice/ |
| Use a selected private key | scp -i ~/.ssh/id_ed25519 report.txt alice@example.net:/home/alice/ |
| Show diagnostics | scp -v report.txt alice@example.net:/home/alice/ |
| Select legacy SCP/rcp protocol | scp -O report.txt alice@example.net:/home/alice/ |
| Generate an Ed25519 key | ssh-keygen -t ed25519 |
| Install a public key | ssh-copy-id alice@example.net |
Which command should you use?
For a one-off upload to a standard SSH server, use the basic local-to-remote form. Add -r only for a directory, -P when the administrator supplied a nonstandard port, and -i when a particular key is required. For repeated transfers, configure an Ed25519 key and a host entry so the command remains short and predictable. Start with the modern default protocol; reserve -O for a confirmed compatibility case. When anything fails, test SSH first, rerun SCP with -v, and consult the remote service log if you administer that server.
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