sudo/docs/sudo.mdoc.in

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.\"	Todd C. Miller <Todd.Miller@sudo.ws>
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.nr SL @SEMAN@
.nr BA @BAMAN@
.nr LC @LCMAN@
.nr PS @PSMAN@
.Dd February 16, 2022
.Dt SUDO @mansectsu@
.Os Sudo @PACKAGE_VERSION@
.Sh NAME
.Nm sudo ,
.Nm sudoedit
.Nd execute a command as another user
.Sh SYNOPSIS
.Nm sudo
.Fl h | K | k | V
.Nm sudo
.Fl v
.Op Fl ABknS
.if \n(BA \{\
.Op Fl a Ar type
.\}
.Op Fl g Ar group
.Op Fl h Ar host
.Op Fl p Ar prompt
.Op Fl u Ar user
.Nm sudo
.Fl l
.Op Fl ABknS
.if \n(BA \{\
.Op Fl a Ar type
.\}
.Op Fl g Ar group
.Op Fl h Ar host
.Op Fl p Ar prompt
.Op Fl U Ar user
.Op Fl u Ar user
.Op Ar command
.Nm sudo
.Op Fl ABbEHnPS
.if \n(BA \{\
.Op Fl a Ar type
.\}
.Op Fl C Ar num
.if \n(LC \{\
.Op Fl c Ar class
.\}
.Op Fl D Ar directory
.Op Fl g Ar group
.Op Fl h Ar host
.Op Fl p Ar prompt
.Op Fl R Ar directory
.if \n(SL \{\
.Op Fl r Ar role
.Op Fl t Ar type
.\}
.Op Fl T Ar timeout
.Op Fl u Ar user
.Op Ar VAR Ns = Ns Ar value
.Op Fl i | s
.Op Ar command
.Nm sudoedit
.Op Fl ABknS
.if \n(BA \{\
.Op Fl a Ar type
.\}
.Op Fl C Ar num
.if \n(LC \{\
.Op Fl c Ar class
.\}
.Op Fl D Ar directory
.Op Fl g Ar group
.Op Fl h Ar host
.Op Fl p Ar prompt
.Op Fl R Ar directory
.if \n(SL \{\
.Op Fl r Ar role
.Op Fl t Ar type
.\}
.Op Fl T Ar timeout
.Op Fl u Ar user
.Ar
.Sh DESCRIPTION
.Nm
allows a permitted user to execute a
.Ar command
as the superuser or another user, as specified by the security
policy.
The invoking user's real
.Pq Em not No effective
user-ID is used to determine the user name with which
to query the security policy.
.Pp
.Nm
supports a plugin architecture for security policies, auditing,
and input/output logging.
Third parties can develop and distribute their own plugins to work
seamlessly with the
.Nm
front-end.
The default security policy is
.Em sudoers ,
which is configured via the file
.Pa @sysconfdir@/sudoers ,
or via LDAP.
See the
.Sx Plugins
section for more information.
.Pp
The security policy determines what privileges, if any, a user has
to run
.Nm .
The policy may require that users authenticate themselves with a
password or another authentication mechanism.
If authentication is required,
.Nm
will exit if the user's password is not entered within a configurable
time limit.
This limit is policy-specific; the default password prompt timeout
for the
.Em sudoers
security policy is
.Li @password_timeout@
minutes.
.Pp
Security policies may support credential caching to allow the user
to run
.Nm
again for a period of time without requiring authentication.
By default, the
.Em sudoers
policy caches credentials on a per-terminal basis for
.Li @timeout@
minutes.
See the
.Em timestamp_type
and
.Em timestamp_timeout
options in
.Xr sudoers @mansectform@
for more information.
By running
.Nm
with the
.Fl v
option, a user can update the cached credentials without running a
.Ar command .
.Pp
On systems where
.Nm
is the primary method of gaining superuser privileges, it is imperative
to avoid syntax errors in the security policy configuration files.
For the default security policy,
.Xr sudoers @mansectform@ ,
changes to the configuration files should be made using the
.Xr visudo @mansectsu@
utility which will ensure that no syntax errors are introduced.
.Pp
When invoked as
.Nm sudoedit ,
the
.Fl e
option (described below), is implied.
.Pp
Security policies and audit plugins may log successful and failed attempts
to run
.Nm .
If an I/O plugin is configured, the running command's input and
output may be logged as well.
.Pp
The options are as follows:
.Bl -tag -width Fl
.It Fl A , -askpass
Normally, if
.Nm
requires a password, it will read it from the user's terminal.
If the
.Fl A Pq Em askpass
option is specified, a (possibly graphical) helper program is
executed to read the user's password and output the password to the
standard output.
If the
.Ev SUDO_ASKPASS
environment variable is set, it specifies the path to the helper
program.
Otherwise, if
.Xr sudo.conf @mansectform@
contains a line specifying the askpass program, that value will be
used.
For example:
.Bd -literal -offset 4n
# Path to askpass helper program
Path askpass /usr/X11R6/bin/ssh-askpass
.Ed
.Pp
If no askpass program is available,
.Nm
will exit with an error.
.if \n(BA \{\
.It Fl a Ar type , Fl -auth-type Ns = Ns Ar type
Use the specified
.Bx
authentication
.Ar type
when validating the user, if allowed by
.Pa /etc/login.conf .
The system administrator may specify a list of sudo-specific
authentication methods by adding an
.Dq auth-sudo
entry in
.Pa /etc/login.conf .
This option is only available on systems that support
.Bx
authentication.
.\}
.It Fl B , -bell
Ring the bell as part of the password prompt when a terminal is present.
This option has no effect if an askpass program is used.
.It Fl b , -background
Run the given command in the background.
It is not possible to use shell job control to manipulate background
processes started by
.Nm .
Most interactive commands will fail to work properly in background
mode.
.It Fl C Ar num , Fl -close-from Ns = Ns Ar num
Close all file descriptors greater than or equal to
.Ar num
before executing a command.
Values less than three are not permitted.
By default,
.Nm
will close all open file descriptors other than standard input,
standard output, and standard error when executing a command.
The security policy may restrict the user's ability to use this option.
The
.Em sudoers
policy only permits use of the
.Fl C
option when the administrator has enabled the
.Em closefrom_override
option.
.if \n(LC \{\
.It Fl c Ar class , Fl -login-class Ns = Ns Ar class
Run the command with resource limits and scheduling priority of
the specified login
.Ar class .
The
.Ar class
argument can be either a class name as defined in
.Pa /etc/login.conf ,
or a single
.Ql \-
character.
If
.Ar class
is
.Cm - ,
the default login class of the target user will be used.
Otherwise, the command must be run as the superuser (user-ID 0), or
.Nm
must be run from a shell that is already running as the superuser.
If the command is being run as a login shell, additional
.Pa /etc/login.conf
settings, such as the umask and environment variables, will
be applied, if present.
This option is only available on systems with
.Bx
login classes.
.\}
.It Fl D Ar directory , Fl -chdir Ns = Ns Ar directory
Run the command in the specified
.Ar directory
instead of the current working directory.
The security policy may return an error if the user does not have
permission to specify the working directory.
.It Fl E , -preserve-env
Indicates to the security policy that the user wishes to
preserve their existing environment variables.
The security policy may return an error if the user does not have
permission to preserve the environment.
.It Fl -preserve-env=list
Indicates to the security policy that the user wishes to add the
comma-separated list of environment variables to those preserved
from the user's environment.
The security policy may return an error if the user does not have
permission to preserve the environment.
This option may be specified multiple times.
.It Fl e , -edit
Edit one or more files instead of running a command.
In lieu of a path name, the string "sudoedit" is used when consulting
the security policy.
If the user is authorized by the policy, the following steps are
taken:
.Bl -enum -offset 4
.It
Temporary copies are made of the files to be edited with the owner
set to the invoking user.
.It
The editor specified by the policy is run to edit the temporary
files.
The
.Em sudoers
policy uses the
.Ev SUDO_EDITOR ,
.Ev VISUAL
and
.Ev EDITOR
environment variables (in that order).
If none of
.Ev SUDO_EDITOR ,
.Ev VISUAL
or
.Ev EDITOR
are set, the first program listed in the
.Em editor
.Xr sudoers @mansectform@
option is used.
.It
If they have been modified, the temporary files are copied back to
their original location and the temporary versions are removed.
.El
.Pp
To help prevent the editing of unauthorized files, the following
restrictions are enforced unless explicitly allowed by the security policy:
.Bl -bullet -offset 4 -width 1n
.It
Symbolic links may not be edited (version 1.8.15 and higher).
.It
Symbolic links along the path to be edited are not followed when the
parent directory is writable by the invoking user unless that user
is root (version 1.8.16 and higher).
.It
Files located in a directory that is writable by the invoking user may
not be edited unless that user is root (version 1.8.16 and higher).
.El
.Pp
Users are never allowed to edit device special files.
.Pp
If the specified file does not exist, it will be created.
Unlike most commands run by
.Em sudo ,
the editor is run with the invoking user's environment unmodified.
If the temporary file becomes empty after editing, the user will
be prompted before it is installed.
If, for some reason,
.Nm
is unable to update a file with its edited version, the user will
receive a warning and the edited copy will remain in a temporary
file.
.It Fl g Ar group , Fl -group Ns = Ns Ar group
Run the command with the primary group set to
.Ar group
instead of the primary group specified by the target
user's password database entry.
The
.Ar group
may be either a group name or a numeric group-ID
.Pq GID
prefixed with the
.Ql #
character (e.g.,
.Li #0
for GID 0).
When running a command as a GID, many shells require that the
.Ql #
be escaped with a backslash
.Pq Ql \e .
If no
.Fl u
option is specified, the command will be run as the invoking user.
In either case, the primary group will be set to
.Ar group .
The
.Em sudoers
policy permits any of the target user's groups to be specified via
the
.Fl g
option as long as the
.Fl P
option is not in use.
.It Fl H , -set-home
Request that the security policy set the
.Ev HOME
environment variable to the home directory specified by the target
user's password database entry.
Depending on the policy, this may be the default behavior.
.It Fl h , -help
Display a short help message to the standard output and exit.
.It Fl h Ar host , Fl -host Ns = Ns Ar host
Run the command on the specified
.Ar host
if the security policy plugin supports remote commands.
The
.Em sudoers
plugin does not currently support running remote commands.
This may also be used in conjunction with the
.Fl l
option to list a user's privileges for the remote host.
.It Fl i , -login
Run the shell specified by the target user's password database entry
as a login shell.
This means that login-specific resource files such as
.Pa .profile ,
.Pa .bash_profile ,
or
.Pa .login
will be read by the shell.
If a command is specified, it is passed to the shell as a simple
command using the
.Fl c
option.
The command and any arguments are concatenated, separated by spaces,
after escaping each character
.Pq including white space
with a backslash
.Pq Ql \e
except for alphanumerics, underscores,
hyphens, and dollar signs.
If no command is specified, an interactive shell is executed.
.Nm
attempts to change to that user's home directory before running the
shell.
The command is run with an environment similar to the one
a user would receive at log in.
Most shells behave differently when a command is specified
as compared to an interactive session; consult the shell's manual
for details.
The
.Em Command environment
section in the
.Xr sudoers @mansectform@
manual documents how the
.Fl i
option affects the environment in which a command is run when the
.Em sudoers
policy is in use.
.It Fl K , -remove-timestamp
Similar to the
.Fl k
option, except that it removes the user's cached credentials entirely
and may not be used in conjunction with a command or other option.
This option does not require a password.
Not all security policies support credential caching.
.It Fl k , -reset-timestamp
When used without a command, invalidates the user's cached credentials.
In other words, the next time
.Nm
is run a password will be required.
This option does not require a password, and was added to allow a
user to revoke
.Nm
permissions from a
.Pa .logout
file.
.Pp
When used in conjunction with a command or an option that may require
a password, this option will cause
.Nm
to ignore the user's cached credentials.
As a result,
.Nm
will prompt for a password (if one is required by the security
policy) and will not update the user's cached credentials.
.Pp
Not all security policies support credential caching.
.It Fl l , Fl -list
If no
.Ar command
is specified,
list the allowed (and forbidden) commands for the
invoking user (or the user specified by the
.Fl U
option) on the current host.
A longer list format is used if this option is specified multiple times
and the security policy supports a verbose output format.
.Pp
If a
.Ar command
is specified and is permitted by the security policy, the fully-qualified
path to the command is displayed along with any command line
arguments.
If a
.Ar command
is specified but not allowed by the policy,
.Nm
will exit with a status value of 1.
.It Fl n , -non-interactive
Avoid prompting the user for input of any kind.
If a password is required for the command to run,
.Nm
will display an error message and exit.
.It Fl P , -preserve-groups
Preserve the invoking user's group vector unaltered.
By default, the
.Em sudoers
policy will initialize the group vector to the list of groups the
target user is a member of.
The real and effective group-IDs, however, are still set to match
the target user.
.It Fl p Ar prompt , Fl -prompt Ns = Ns Ar prompt
Use a custom password prompt with optional escape sequences.
The following percent
.Pq Ql %
escape sequences are supported by the
.Em sudoers
policy:
.Bl -tag -width 2n
.It Li %H
expanded to the host name including the domain name (only if the
machine's host name is fully qualified or the
.Em fqdn
option is set in
.Xr sudoers @mansectform@ )
.It Li %h
expanded to the local host name without the domain name
.It Li %p
expanded to the name of the user whose password is being requested
(respects the
.Em rootpw ,
.Em targetpw ,
and
.Em runaspw
flags in
.Xr sudoers @mansectform@ )
.It Li \&%U
expanded to the login name of the user the command will be run as
(defaults to root unless the
.Fl u
option is also specified)
.It Li %u
expanded to the invoking user's login name
.It Li %%
two consecutive
.Ql %
characters are collapsed into a single
.Ql %
character
.El
.Pp
The custom prompt will override the default prompt specified by either
the security policy or the
.Ev SUDO_PROMPT
environment variable.
On systems that use PAM, the custom prompt will also override the prompt
specified by a PAM module unless the
.Em passprompt_override
flag is disabled in
.Em sudoers .
.It Fl R Ar directory , Fl -chroot Ns = Ns Ar directory
Change to the specified root
.Ar directory
(see
.Xr chroot @mansectsu@ )
before running the command.
The security policy may return an error if the user does not have
permission to specify the root directory.
.if \n(SL \{\
.It Fl r Ar role , Fl -role Ns = Ns Ar role
Run the command with an SELinux security context that includes
the specified
.Ar role .
.\}
.It Fl S , -stdin
Write the prompt to the standard error and read the password from the
standard input instead of using the terminal device.
.It Fl s , -shell
Run the shell specified by the
.Ev SHELL
environment variable if it is set or the shell specified by the
invoking user's password database entry.
If a command is specified, it is passed to the shell as a simple
command using the
.Fl c
option.
The command and any arguments are concatenated, separated by spaces,
after escaping each character
.Pq including white space
with a backslash
.Pq Ql \e
except for alphanumerics, underscores,
hyphens, and dollar signs.
If no command is specified, an interactive shell is executed.
Most shells behave differently when a command is specified
as compared to an interactive session; consult the shell's manual
for details.
.if \n(SL \{\
.It Fl t Ar type , Fl -type Ns = Ns Ar type
Run the command with an SELinux security context that includes
the specified
.Ar type .
If no
.Ar type
is specified, the default type is derived from the role.
.\}
.It Fl U Ar user , Fl -other-user Ns = Ns Ar user
Used in conjunction with the
.Fl l
option to list the privileges for
.Ar user
instead of for the invoking user.
The security policy may restrict listing other users' privileges.
When using the
.Em sudoers
policy, only root or a user with the ability to run any command as
either root or the specified
.Ar user
on the current host may use this option.
.It Fl T Ar timeout , Fl -command-timeout Ns = Ns Ar timeout
Used to set a timeout for the command.
If the timeout expires before the command has exited, the
command will be terminated.
The security policy may restrict the ability to set command timeouts.
The
.Em sudoers
policy requires that user-specified timeouts be explicitly enabled.
.It Fl u Ar user , Fl -user Ns = Ns Ar user
Run the command as a user other than the default target user
(usually
.Em root ) .
The
.Ar user
may be either a user name or a numeric user-ID
.Pq UID
prefixed with the
.Ql #
character (e.g.,
.Li #0
for UID 0).
When running commands as a UID, many shells require that the
.Ql #
be escaped with a backslash
.Pq Ql \e .
Some security policies may restrict UIDs
to those listed in the password database.
The
.Em sudoers
policy allows UIDs that are not in the password database as long as the
.Em targetpw
option is not set.
Other security policies may not support this.
.It Fl V , -version
Print the
.Nm
version string as well as the version string of any configured plugins.
If the invoking user is already root, the
.Fl V
option will display the arguments passed to configure when
.Nm
was built; plugins may display additional information such as
default options.
.It Fl v , -validate
Update the user's cached credentials, authenticating the user
if necessary.
For the
.Em sudoers
plugin, this extends the
.Nm
timeout for another
.Li @timeout@
minutes by default, but does not run a command.
Not all security policies support cached credentials.
.It Fl -
The
.Fl -
option indicates that
.Nm
should stop processing command line arguments.
.El
.Pp
Options that take a value may only be specified once unless
otherwise indicated in the description.
This is to help guard against problems caused by poorly written
scripts that invoke
.Nm sudo
with user-controlled input.
.Pp
Environment variables to be set for the command may also be passed
on the command line in the form of
.Ar VAR Ns = Ns Ar value ,
e.g.,
.Ev LD_LIBRARY_PATH Ns = Ns Pa /usr/local/pkg/lib .
Variables passed on the command line are subject to restrictions
imposed by the security policy plugin.
The
.Em sudoers
policy subjects variables passed on the command line to the same
restrictions as normal environment variables with one important
exception.
If the
.Em setenv
option is set in
.Em sudoers ,
the command to be run has the
.Li SETENV
tag set or the command matched is
.Li ALL ,
the user may set variables that would otherwise be forbidden.
See
.Xr sudoers @mansectform@
for more information.
.Sh COMMAND EXECUTION
When
.Nm
executes a command, the security policy specifies the execution
environment for the command.
Typically, the real and effective user and group and IDs are set to
match those of the target user, as specified in the password database,
and the group vector is initialized based on the group database
(unless the
.Fl P
option was specified).
.Pp
The following parameters may be specified by security policy:
.Bl -bullet -width 1n
.It
real and effective user-ID
.It
real and effective group-ID
.It
supplementary group-IDs
.It
the environment list
.It
current working directory
.It
file creation mode mask (umask)
.if \n(SL \{\
.It
SELinux role and type
.\}
.if \n(PS \{\
.It
Solaris project
.It
Solaris privileges
.\}
.if \n(LC \{\
.It
.Bx
login class
.\}
.It
scheduling priority (aka nice value)
.El
.Ss Process model
There are two distinct ways
.Nm
can run a command.
.Pp
If an I/O logging plugin is configured or if the security policy
explicitly requests it, a new pseudo-terminal
.Pq Dq pty
is allocated and
.Xr fork 2
is used to create a second
.Nm
process, referred to as the
.Em monitor .
The
.Em monitor
creates a new terminal session with itself as the leader and the pty as its
controlling terminal, calls
.Xr fork 2 ,
sets up the execution environment as described above, and then uses the
.Xr execve 2
system call to run the command in the child process.
The
.Em monitor
exists to relay job control signals between the user's
existing terminal and the pty the command is being run in.
This makes it possible to suspend and resume the command.
Without the monitor, the command would be in what POSIX terms an
.Dq orphaned process group
and it would not receive any job control signals from the kernel.
When the command exits or is terminated by a signal, the
.Em monitor
passes the command's exit status to the main
.Nm
process and exits.
After receiving the command's exit status, the main
.Nm
passes the command's exit status to the security policy's close function
and exits.
.Pp
If no pty is used,
.Nm
calls
.Xr fork 2 ,
sets up the execution environment as described above, and uses the
.Xr execve 2
system call to run the command in the child process.
The main
.Nm
process waits until the command has completed, then passes the
command's exit status to the security policy's close function and exits.
As a special case, if the policy plugin does not define a close
function,
.Nm
will execute the command directly instead of calling
.Xr fork 2
first.
The
.Em sudoers
policy plugin will only define a close function when I/O logging
is enabled, a pty is required, an SELinux role is specified, the
command has an associated timeout, or the
.Em pam_session
or
.Em pam_setcred
options are enabled.
Both
.Em pam_session
and
.Em pam_setcred
are enabled by default on systems using PAM.
.Pp
On systems that use PAM, the security policy's close function
is responsible for closing the PAM session.
It may also log the command's exit status.
.Ss Signal handling
When the command is run as a child of the
.Nm
process,
.Nm
will relay signals it receives to the command.
The
.Dv SIGINT
and
.Dv SIGQUIT
signals are only relayed when the command is being run in a new pty
or when the signal was sent by a user process, not the kernel.
This prevents the command from receiving
.Dv SIGINT
twice each time the user enters control-C.
Some signals, such as
.Dv SIGSTOP
and
.Dv SIGKILL ,
cannot be caught and thus will not be relayed to the command.
As a general rule,
.Dv SIGTSTP
should be used instead of
.Dv SIGSTOP
when you wish to suspend a command being run by
.Nm .
.Pp
As a special case,
.Nm
will not relay signals that were sent by the command it is running.
This prevents the command from accidentally killing itself.
On some systems, the
.Xr reboot @mansectsu@
command sends
.Dv SIGTERM
to all non-system processes other than itself before rebooting
the system.
This prevents
.Nm
from relaying the
.Dv SIGTERM
signal it received back to
.Xr reboot @mansectsu@ ,
which might then exit before the system was actually rebooted,
leaving it in a half-dead state similar to single user mode.
Note, however, that this check only applies to the command run by
.Nm
and not any other processes that the command may create.
As a result, running a script that calls
.Xr reboot @mansectsu@
or
.Xr shutdown @mansectsu@
via
.Nm
may cause the system to end up in this undefined state unless the
.Xr reboot @mansectsu@
or
.Xr shutdown @mansectsu@
are run using the
.Fn exec
family of functions instead of
.Fn system
(which interposes a shell between the command and the calling process).
.Pp
If no I/O logging plugins are loaded and the policy plugin has not
defined a
.Fn close
function, set a command timeout, or required that the command be
run in a new pty,
.Nm
may execute the command directly instead of running it as a child process.
.Ss Plugins
Plugins may be specified via
.Li Plugin
directives in the
.Xr sudo.conf @mansectform@
file.
They may be loaded as dynamic shared objects (on systems that support them),
or compiled directly into the
.Nm
binary.
If no
.Xr sudo.conf @mansectform@
file is present, or if it doesn't contain any
.Li Plugin
lines,
.Nm
will use
.Xr sudoers @mansectform@
for the policy, auditing, and I/O logging plugins.
See the
.Xr sudo.conf @mansectform@
manual for details of the
.Pa @sysconfdir@/sudo.conf
file and the
.Xr sudo_plugin @mansectform@
manual for more information about the
.Nm
plugin architecture.
.Sh EXIT VALUE
Upon successful execution of a command, the exit status from
.Nm
will be the exit status of the program that was executed.
If the command terminated due to receipt of a signal,
.Nm
will send itself the same signal that terminated the command.
.Pp
If the
.Fl l
option was specified without a command,
.Nm
will exit with a value of 0 if the user is allowed to run
.Nm
and they authenticated successfully (as required by the security policy).
If a command is specified with the
.Fl l
option, the exit value will only be 0 if the command is permitted by the
security policy, otherwise it will be 1.
.Pp
If there is an authentication failure, a configuration/permission
problem, or if the given command cannot be executed,
.Nm
exits with a value of 1.
In the latter case, the error string is printed to the standard error.
If
.Nm
cannot
.Xr stat 2
one or more entries in the user's
.Ev PATH ,
an error is printed to the standard error.
(If the directory does not exist or if it is not really a directory,
the entry is ignored and no error is printed.)
This should not happen under normal circumstances.
The most common reason for
.Xr stat 2
to return
.Dq permission denied
is if you are running an automounter and one of the directories in
your
.Ev PATH
is on a machine that is currently unreachable.
.Sh SECURITY NOTES
.Nm
tries to be safe when executing external commands.
.Pp
To prevent command spoofing,
.Nm
checks "." and "" (both denoting current directory) last when
searching for a command in the user's
.Ev PATH
(if one or both are in the
.Ev PATH ) .
Depending on the security policy, the user's
.Ev PATH
environment variable may be modified, replaced,
or passed unchanged to the program that
.Nm
executes.
.Pp
Users should
.Em never
be granted
.Nm
privileges to execute files that are writable by the user or
that reside in a directory that is writable by the user.
If the user can modify or replace the command there is no way
to limit what additional commands they can run.
.Pp
By default,
.Nm
will only log the command it explicitly runs.
If a user runs a command such as
.Li sudo su
or
.Li sudo sh ,
subsequent commands run from that shell are not subject to
.Nm sudo Ns 's
security policy.
The same is true for commands that offer shell escapes (including
most editors).
If I/O logging is enabled, subsequent commands will have their input and/or
output logged, but there will not be traditional logs for those commands.
Because of this, care must be taken when giving users access to commands via
.Nm
to verify that the command does not inadvertently give the user an
effective root shell.
For information on ways to address this, see the
.Em Preventing shell escapes
section in
.Xr sudoers @mansectform@ .
.Pp
To prevent the disclosure of potentially sensitive information,
.Nm
disables core dumps by default while it is executing (they are
re-enabled for the command that is run).
This historical practice dates from a time when most operating
systems allowed set-user-ID processes to dump core by default.
To aid in debugging
.Nm
crashes, you may wish to re-enable core dumps by setting
.Dq disable_coredump
to false in the
.Xr sudo.conf @mansectform@
file as follows:
.Bd -literal -offset 4n
Set disable_coredump false
.Ed
.Pp
See the
.Xr sudo.conf @mansectform@
manual for more information.
.Sh ENVIRONMENT
.Nm
utilizes the following environment variables.
The security policy has control over the actual content of the command's
environment.
.Bl -tag -width 15n
.It Ev EDITOR
Default editor to use in
.Fl e
(sudoedit) mode if neither
.Ev SUDO_EDITOR
nor
.Ev VISUAL
is set.
.It Ev MAIL
Set to the mail spool of the target user when the
.Fl i
option is specified, or when
.Em env_reset
is enabled in
.Em sudoers
(unless
.Ev MAIL
is present in the
.Em env_keep
list).
.It Ev HOME
Set to the home directory of the target user when the
.Fl i
or
.Fl H
options are specified, when the
.Fl s
option is specified and
.Em set_home
is set in
.Em sudoers ,
when
.Em always_set_home
is enabled in
.Em sudoers ,
or when
.Em env_reset
is enabled in
.Em sudoers
and
.Em HOME
is not present in the
.Em env_keep
list.
.It Ev LOGNAME
Set to the login name of the target user when the
.Fl i
option is specified, when the
.Em set_logname
option is enabled in
.Em sudoers ,
or when the
.Em env_reset
option is enabled in
.Em sudoers
(unless
.Ev LOGNAME
is present in the
.Em env_keep
list).
.It Ev PATH
May be overridden by the security policy.
.It Ev SHELL
Used to determine shell to run with
.Fl s
option.
.It Ev SUDO_ASKPASS
Specifies the path to a helper program used to read the password
if no terminal is available or if the
.Fl A
option is specified.
.It Ev SUDO_COMMAND
Set to the command run by sudo, including command line arguments.
The command line arguments are truncated at 4096 characters to
prevent a potential execution error.
.It Ev SUDO_EDITOR
Default editor to use in
.Fl e
(sudoedit) mode.
.It Ev SUDO_GID
Set to the group-ID of the user who invoked sudo.
.It Ev SUDO_PROMPT
Used as the default password prompt unless
the
.Fl p
option was specified.
.It Ev SUDO_PS1
If set,
.Ev PS1
will be set to its value for the program being run.
.It Ev SUDO_UID
Set to the user-ID of the user who invoked sudo.
.It Ev SUDO_USER
Set to the login name of the user who invoked sudo.
.It Ev USER
Set to the same value as
.Ev LOGNAME ,
described above.
.It Ev VISUAL
Default editor to use in
.Fl e
(sudoedit) mode if
.Ev SUDO_EDITOR
is not set.
.El
.Sh FILES
.Bl -tag -width 24n
.It Pa @sysconfdir@/sudo.conf
.Nm
front-end configuration
.El
.Sh EXAMPLES
The following examples assume a properly configured security policy.
.Pp
To get a file listing of an unreadable directory:
.Bd -literal -offset 4n
$ sudo ls /usr/local/protected
.Ed
.Pp
To list the home directory of user yaz on a machine where the file
system holding ~yaz is not exported as root:
.Bd -literal -offset 4n
$ sudo -u yaz ls ~yaz
.Ed
.Pp
To edit the
.Pa index.html
file as user www:
.Bd -literal -offset 4n
$ sudoedit -u www ~www/htdocs/index.html
.Ed
.Pp
To view system logs only accessible to root and users in the adm
group:
.Bd -literal -offset 4n
$ sudo -g adm more @log_dir@/syslog
.Ed
.Pp
To run an editor as jim with a different primary group:
.Bd -literal -offset 4n
$ sudoedit -u jim -g audio ~jim/sound.txt
.Ed
.Pp
To shut down a machine:
.Bd -literal -offset 4n
$ sudo shutdown -r +15 "quick reboot"
.Ed
.Pp
To make a usage listing of the directories in the /home partition.
The commands are run in a sub-shell to allow the
.Li cd
command and file redirection to work.
.Bd -literal -offset 4n
$ sudo sh -c "cd /home ; du -s * | sort -rn > USAGE"
.Ed
.Sh DIAGNOSTICS
Error messages produced by
.Nm
include:
.Bl -tag -width 4n
.It Li editing files in a writable directory is not permitted
By default,
.Nm sudoedit
does not permit editing a file when any of the parent directories are writable
by the invoking user.
This avoids a race condition that could allow the user to overwrite
an arbitrary file.
See the
.Em sudoedit_checkdir
option in
.Xr sudoers @mansectform@
for more information.
.It Li editing symbolic links is not permitted
By default,
.Nm sudoedit
does not follow symbolic links when opening files.
See the
.Em sudoedit_follow
option in
.Xr sudoers @mansectform@
for more information.
.It Li effective uid is not 0, is sudo installed setuid root?
.Nm
was not run with root privileges.
The
.Nm
binary must be owned by the root user and have the set-user-ID bit set.
Also, it must not be located on a file system mounted with the
.Sq nosuid
option or on an NFS file system that maps uid 0 to an unprivileged uid.
.It Li effective uid is not 0, is sudo on a file system with the 'nosuid' option set or an NFS file system without root privileges?
.Nm
was not run with root privileges.
The
.Nm
binary has the proper owner and permissions but it still did not run
with root privileges.
The most common reason for this is that the file system the
.Nm
binary is located on is mounted with the
.Sq nosuid
option or it is an NFS file system that maps uid 0 to an unprivileged uid.
.It Li fatal error, unable to load plugins
An error occurred while loading or initializing the plugins specified in
.Xr sudo.conf @mansectform@ .
.It Li invalid environment variable name
One or more environment variable names specified via the
.Fl E
option contained an equal sign
.Pq Ql = .
The arguments to the
.Fl E
option should be environment variable names without an associated value.
.It Li no password was provided
When
.Nm
tried to read the password, it did not receive any characters.
This may happen if no terminal is available (or the
.Fl S
option is specified) and the standard input has been redirected from
.Pa /dev/null .
.It Li a terminal is required to read the password
.Nm
needs to read the password but there is no mechanism available for it
to do so.
A terminal is not present to read the password from,
.Nm
has not been configured to read from the standard input,
the
.Fl S
option was not used, and no askpass helper has been specified either via the
.Xr sudo.conf @mansectform@
file or the
.Ev SUDO_ASKPASS
environment variable.
.It Li no writable temporary directory found
.Nm sudoedit
was unable to find a usable temporary directory in which to store its
intermediate files.
.It Li The Do "no new privileges" Dc "flag is set, which prevents sudo from running as root."
.Nm
was run by a process that has the Linux
.Dq no new privileges
flag is set.
This causes the set-user-ID bit to be ignored when running an executable,
which will prevent
.Nm
from functioning.
The most likely cause for this is running
.Nm
within a container that sets this flag.
Check the documentation to see if it is possible to configure the
container such that the flag is not set.
.It Li sudo must be owned by uid 0 and have the setuid bit set
.Nm
was not run with root privileges.
The
.Nm
binary does not have the correct owner or permissions.
It must be owned by the root user and have the set-user-ID bit set.
.It Li sudoedit is not supported on this platform
It is only possible to run
.Nm sudoedit
on systems that support setting the effective user-ID.
.It Li timed out reading password
The user did not enter a password before the password timeout
(5 minutes by default) expired.
.It Li you do not exist in the passwd database
Your user-ID does not appear in the system passwd database.
.It Li you may not specify environment variables in edit mode
It is only possible to specify environment variables when running
a command.
When editing a file, the editor is run with the user's environment unmodified.
.El
.Sh SEE ALSO
.Xr su 1 ,
.Xr stat 2 ,
.Xr login_cap 3 ,
.Xr passwd @mansectform@ ,
.Xr sudo.conf @mansectform@ ,
.Xr sudo_plugin @mansectform@ ,
.Xr sudoers @mansectform@ ,
.Xr sudoers_timestamp @mansectform@ ,
.Xr sudoreplay @mansectsu@ ,
.Xr visudo @mansectsu@
.Sh HISTORY
See the HISTORY.md file in the
.Nm
distribution (https://www.sudo.ws/about/history/) for a brief
history of sudo.
.Sh AUTHORS
Many people have worked on
.Nm
over the years; this version consists of code written primarily by:
.Bd -ragged -offset indent
.An Todd C. Miller
.Ed
.Pp
See the CONTRIBUTORS.md file in the
.Nm
distribution (https://www.sudo.ws/about/contributors/) for an
exhaustive list of people who have contributed to
.Nm .
.Sh CAVEATS
There is no easy way to prevent a user from gaining a root shell
if that user is allowed to run arbitrary commands via
.Nm .
Also, many programs (such as editors) allow the user to run commands
via shell escapes, thus avoiding
.Nm sudo Ns 's
checks.
However, on most systems it is possible to prevent shell escapes with the
.Xr sudoers @mansectform@
plugin's
.Em noexec
functionality.
.Pp
It is not meaningful to run the
.Li cd
command directly via sudo, e.g.,
.Bd -literal -offset 4n
$ sudo cd /usr/local/protected
.Ed
.Pp
since when the command exits the parent process (your shell) will
still be the same.
See the
.Sx EXAMPLES
section for more information.
.Pp
Running shell scripts via
.Nm
can expose the same kernel bugs that make set-user-ID shell scripts
unsafe on some operating systems (if your OS has a /dev/fd/ directory,
set-user-ID shell scripts are generally safe).
.Sh BUGS
If you believe you have found a bug in
.Nm ,
you can submit a bug report at https://bugzilla.sudo.ws/
.Sh SUPPORT
Limited free support is available via the sudo-users mailing list,
see https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or
search the archives.
.Sh DISCLAIMER
.Nm
is provided
.Dq AS IS
and any express or implied warranties, including, but not limited
to, the implied warranties of merchantability and fitness for a
particular purpose are disclaimed.
See the LICENSE.md file distributed with
.Nm
or https://www.sudo.ws/about/license/ for complete details.