VTY shell — FRR 9.1/frr-9.1 documentation

# VTY shell

vtysh provides a combined frontend to all FRR daemons in a single combined session. It is enabled by default at build time, but can be disabled through the `--disable-vtysh` option to the configure script.

vtysh has a configuration file, `vtysh.conf`. The location of that file cannot be changed from /etc/frr since it contains options controlling authentication behavior. This file will also not be written by configuration-save commands, it is intended to be updated manually by an administrator with an external editor.

Warning

This also means the `hostname`, `domainname`, and `banner motd` commands (which do have effect for vtysh) need to be manually updated in `vtysh.conf`.

copy FILENAME running-config

  Process and load a configuration file manually; each line in the file is read and processed as if it were being typed (or piped) to vtysh.

## Live logs

terminal monitor [DAEMON]

  Receive and display log messages.

  It is not currently possible to change the minimum message priority (fixed to debug) or output formatting. These will likely be made configurable in the future.

  Log messages are received asynchronously and may be printed both during command execution as well as while on the prompt. They are printed to stderr, unlike regular CLI output which is printed to stdout. The intent is that stdin/stdout might be driven by some script while log messages are visible on stderr. If stdout and stderr are the same file, the prompt and pending input will be cleared and reprinted appropriately.

  Note

  If `vtysh` cannot keep up, some log messages may be lost. The daemons do not wait for, get blocked by, or buffer messages for `vtysh`.

## Pager usage

vtysh can call an external paging program (e.g. more or less) to paginate long output from commands. This feature used to be enabled by default but is now controlled by the `VTYSH_PAGER` environment variable and the `terminal paginate` command:

VTYSH_PAGER

  If set, the `VTYSH_PAGER` environment variable causes vtysh to pipe output from commands through the given command. Note that this happens regardless of the length of the output. As such, standard pager behavior (particularly waiting at the end of output) tends to be annoying to the user. Using `less -EFX` is recommended for a better user experience.

  If this environment variable is unset, vtysh defaults to not using any pager.

  This variable should be set by the user according to their preferences, in their `~/.profile` file.

terminal paginate

  Enables/disables vtysh output pagination. This command is intended to be placed in `vtysh.conf` to set a system-wide default. If this is enabled but `VTYSH_PAGER` is not set, the system default pager (likely `more` or `/usr/bin/pager`) will be used.

## Permissions and setup requirements

vtysh connects to running daemons through Unix sockets located in /var/run/frr. Running vtysh thus requires access to that directory, plus membership in the frrvty group (which is the group that the daemons will change ownership of their sockets to).

To restrict access to FRR configuration, make sure no unauthorized users are members of the frrvty group.

Warning

VTYSH implements a CLI option `-u, --user` that disallows entering the characters "en" on the command line, which ideally restricts access to configuration commands. However, VTYSH was never designed to be a privilege broker and is not built using secure coding practices. No guarantees of security are provided for this option and under no circumstances should this option be used to provide any semblance of security or read-only access to FRR.

### PAM support (experimental)

vtysh has working (but rather useless) PAM support. It will perform an "authenticate" PAM call using frr as service name. No other (accounting, session, password change) calls will be performed by vtysh.

Users using vtysh still need to have appropriate access to the daemons' VTY sockets, usually by being member of the frrvty group. If they have this membership, PAM support is useless since they can connect to daemons and issue commands using some other tool. Alternatively, the vtysh binary could be made SGID (set group ID) to the frrvty group.

Warning

No security guarantees are made for this configuration.

username USERNAME nopassword

  If PAM support is enabled at build-time, this command allows disabling the use of PAM on a per-user basis. If vtysh finds that an user is trying to use vtysh and a "nopassword" entry is found, no calls to PAM will be made at all.

## Integrated configuration mode

Integrated configuration mode uses a single configuration file, `frr.conf`, for all daemons. This replaces the individual files like `zebra.conf` or `bgpd.conf`.

`frr.conf` is located in /etc/frr. All daemons check for the existence of this file at startup, and if it exists will not load their individual configuration files. Instead, `vtysh -b` must be invoked to process `frr.conf` and apply its settings to the individual daemons.

Warning

vtysh -b must also be executed after restarting any daemon.

### Configuration saving, file ownership and permissions

The `frr.conf` file is not written by any of the daemons; instead vtysh contains the necessary logic to collect configuration from all of the daemons, combine it and write it out.

Warning

Daemons must be running for vtysh to be able to collect their configuration. Any configuration from non-running daemons is permanently lost after doing a configuration save.

Since the vtysh command may be running as ordinary user on the system, configuration writes will be tried through watchfrr, using the `write integrated` command internally. Since watchfrr is running as superuser, vtysh is able to ensure correct ownership and permissions on `frr.conf`.

If watchfrr is not running or the configuration write fails, vtysh will attempt to directly write to the file. This is likely to fail if running as unprivileged user; alternatively it may leave the file with incorrect owner or permissions.

Writing the configuration can be triggered directly by invoking vtysh -w. This may be useful for scripting. Note this command should be run as either the superuser or the FRR user.

We recommend you do not mix the use of the two types of files.

service integrated-vtysh-config

  Control whether integrated `frr.conf` file is written when 'write file' is issued.

  These commands need to be placed in `vtysh.conf` to have any effect. Note that since `vtysh.conf` is not written by FRR itself, they therefore need to be manually placed in that file.

  This command has 3 states:

  service integrated-vtysh-config

    vtysh will always write `frr.conf`.

  no service integrated-vtysh-config

    vtysh will never write `frr.conf`; instead it will ask daemons to write their individual configuration files.

  Neither option present (default)

    vtysh will check whether `frr.conf` exists. If it does, configuration writes will update that file. Otherwise, writes are performed through the individual daemons.

  This command is primarily intended for packaging/distribution purposes, to preset one of the two operating modes and ensure consistent operation across installations.

write integrated

  Unconditionally (regardless of `service integrated-vtysh-config` setting) write out integrated `frr.conf` file through watchfrr. If watchfrr is not running, this command is unavailable.

Warning

Configuration changes made while some daemon is not running will be invisible to that daemon. The daemon will start up with its saved configuration (either in its individual configuration file, or in `frr.conf`). This is particularly troublesome for route-maps and prefix lists, which would otherwise be synchronized between daemons.