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v1.9.14
docs/sudo.mdoc.in
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Todd C. Miller
Sudo runs the command in a pty by default in 1.9.14 and above.
18 июн 2023, 17:08
18 июн 2023, 17:08
afb09e0
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.\" .\" SPDX-License-Identifier: ISC .\" .\" Copyright (c) 1994-1996, 1998-2005, 2007-2023 .\" Todd C. Miller <Todd.Miller@sudo.ws> .\" .\" Permission to use, copy, modify, and distribute this software for any .\" purpose with or without fee is hereby granted, provided that the above .\" copyright notice and this permission notice appear in all copies. .\" .\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES .\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF .\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR .\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES .\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. .\" .\" Sponsored in part by the Defense Advanced Research Projects .\" Agency (DARPA) and Air Force Research Laboratory, Air Force .\" Materiel Command, USAF, under agreement number F39502-99-1-0512. .\" .nr SL @SEMAN@ .nr BA @BAMAN@ .nr LC @LCMAN@ .nr PS @PSMAN@ .Dd June 18, 2023 .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 ABkNnS .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 ABkNnS .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 Op Ar arg ... .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 Op Ar arg ... .Nm sudoedit .Op Fl ABkNnS .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 @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 @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 .Ar command Ns 's input and output may be logged as well. .Pp The options are as follows: .Bl -tag -width Ds .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 .Ar command in the background. It is not possible to use shell job control to manipulate background processes started by .Nm . Most interactive .Ar command Ns s 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 .Ar 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 .Ar 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 .Ar 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 .Ar 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 .Ar 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 .Ar 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 .Ar file Ns s instead of running a .Ar 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 1n -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 .Ar command Ns s 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 .Ar 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., .Ql #0 for GID 0). When running a .Ar 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 .Ar 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 .Ar command on the specified .Ar host if the security policy plugin supports remote .Ar command Ns s. The .Em sudoers plugin does not currently support running remote .Ar command Ns s. 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 .Ar command is specified, it is passed to the shell as a simple .Ar command using the .Fl c option. The .Ar command and any .Ar arg Ns s 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 .Ar command is specified, an interactive shell is executed. .Nm attempts to change to that user's home directory before running the shell. The .Ar command is run with an environment similar to the one a user would receive at log in. Most shells behave differently when a .Ar 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 .Ar 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 every cached credential for the user, regardless of the terminal or parent process ID. The next time .Nm is run, a password must be entered if the security policy requires authentication. It is not possible to use the .Fl K option in conjunction with a .Ar 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 .Ar command , invalidates the user's cached credentials for the current session. The next time .Nm is run in the session, a password must be entered if the security policy requires authentication. By default, the .Nm sudoers policy uses a separate record in the credential cache for each terminal (or parent process ID if no terminal is present). This prevents the .Fl k option from interfering with .Nm commands run in a different terminal session. See the .Em timestamp_type option in .Xr sudoers @mansectform@ for more information. 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 .Ar 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 privileges for the invoking user (or the .Ar 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 .Ar command is displayed along with any .Ar arg Ns s. If a .Ar command is specified but not allowed by the policy, .Nm will exit with a status value of 1. .It Fl N , -no-update Do not update the user's cached credentials, even if the user successfully authenticates. Unlike the .Fl k flag, existing cached credentials are used if they are valid. To detect when the user's cached credentials are valid (or when no authentication is required), the following can be used: .Dl sudo -Nnv .Pp Not all security policies support credential caching. .It Fl n , -non-interactive Avoid prompting the user for input of any kind. If a password is required for the .Ar 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 %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 %h expanded to the local host name without the domain name .It %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 \&%U expanded to the login name of the user the .Ar command will be run as (defaults to root unless the .Fl u option is also specified) .It %u expanded to the invoking user's login name .It %% 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 .Ar 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 .Ar 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 .Ar command is specified, it is passed to the shell as a simple command using the .Fl c option. The .Ar command and any .Ar arg Ns s 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 .Ar command is specified, an interactive shell is executed. Most shells behave differently when a .Ar 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 .Ar 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, the .Fl U option is restricted to the root user and users with either the .Dq list priviege for the specified .Ar user or the ability to run any .Ar command as root or .Ar user on the current host. .It Fl T Ar timeout , Fl -command-timeout Ns = Ns Ar timeout Used to set a timeout for the .Ar command . If the timeout expires before the .Ar command has exited, the .Ar command will be terminated. The security policy may restrict the user's ability to set 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 .Ar command as a user other than the default target user (usually .Sy root ) . The .Ar user may be either a user name or a numeric user-ID .Pq UID prefixed with the .Ql # character (e.g., .Ql #0 for UID 0). When running .Ar command Ns s 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 options 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 @timeout@ minutes by default, but does not run a .Ar command . Not all security policies support cached credentials. .It Fl - The .Fl - is used to delimit the end of the .Nm options. Subsequent options are passed to the .Ar command . .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 .Ar command may also be passed as options to .Nm in the form .Ar VAR Ns = Ns Ar value , for example .Ev LD_LIBRARY_PATH Ns = Ns Pa /usr/local/pkg/lib . Environment variables may be subject to restrictions imposed by the security policy plugin. The .Em sudoers policy subjects environment variables passed as options to the same restrictions as existing environment variables with one important difference. If the .Em setenv option is set in .Em sudoers , the .Ar command to be run has the .Dv SETENV tag set or the .Ar command matched is .Sy 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 .Ar command , the security policy specifies the execution environment for the .Ar 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 .Ar command . .Pp If an I/O logging plugin is configured to log terminal I/O, 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 again, sets up the execution environment as described above, and then uses the .Xr execve 2 system call to run the .Ar command in the child process. The .Em monitor exists to relay job control signals between the user's terminal and the pty the .Ar command is being run in. This makes it possible to suspend and resume the .Ar command normally. Without the .Em monitor , the .Ar 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 .Ar command exits or is terminated by a signal, the .Em monitor passes the .Ar command Ns 's exit status to the main .Nm process and exits. After receiving the .Ar command Ns 's exit status, the main .Nm process passes the .Ar command Ns 's exit status to the security policy's close function, as well as the close function of any configured audit plugin, and exits. This mode is the default for sudo versions 1.9.14 and above when using the sudoers policy. .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 .Ar command in the child process. The main .Nm process waits until the .Ar command has completed, then passes the .Ar command Ns 's exit status to the security policy's close function, as well as the close function of any configured audit plugins, and exits. As a special case, if the policy plugin does not define a close function, .Nm will execute the .Ar 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 .Ar 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. This mode is the default for sudo versions prior to 1.9.14 when using the sudoers policy. .Pp On systems that use PAM, the security policy's close function is responsible for closing the PAM session. It may also log the .Ar command Ns 's exit status. .Ss Signal handling When the .Ar command is run as a child of the .Nm process, .Nm will relay signals it receives to the .Ar command . The .Dv SIGINT and .Dv SIGQUIT signals are only relayed when the .Ar command is being run in a new pty or when the signal was sent by a user process, not the kernel. This prevents the .Ar 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 .Ar command . As a general rule, .Dv SIGTSTP should be used instead of .Dv SIGSTOP when you wish to suspend a .Ar command being run by .Nm . .Pp As a special case, .Nm will not relay signals that were sent by the .Ar command it is running. This prevents the .Ar command from accidentally killing itself. On some systems, the .Xr reboot @mansectsu@ utility 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 .Ar command run by .Nm and not any other processes that the .Ar 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 .Ar command and the calling process). .Ss Plugins Plugins may be specified via .Em 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 .Em 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 .Ar command , the exit status from .Nm will be the exit status of the program that was executed. If the .Ar command terminated due to receipt of a signal, .Nm will send itself the same signal that terminated the .Ar command . .Pp If the .Fl l option was specified without a .Ar 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 .Ar command is specified with the .Fl l option, the exit value will only be 0 if the .Ar 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 .Ar 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 .Ar command Ns s. .Pp To prevent command spoofing, .Nm checks "." and "" (both denoting current directory) last when searching for a .Ar 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 .Ar command there is no way to limit what additional .Ar command Ns s they can run. .Pp By default, .Nm will only log the .Ar command it explicitly runs. If a user runs a .Ar command such as .Ql sudo su or .Ql sudo sh , subsequent .Ar command Ns s run from that shell are not subject to .Nm sudo Ns 's security policy. The same is true for .Ar command Ns s that offer shell escapes (including most editors). If I/O logging is enabled, subsequent .Ar command Ns s will have their input and/or output logged, but there will not be traditional logs for those .Ar command Ns s. Because of this, care must be taken when giving users access to .Ar command Ns s via .Nm to verify that the .Ar 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 .Ar 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 .Ar command Ns '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 .Ev 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 .Ar command run by sudo, including any .Ar arg Ns s. The .Ar arg Ns s 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 .Ar commands are run in a sub-shell to allow the .Ql 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 .Ar 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 .Ar commands via .Nm . Also, many programs (such as editors) allow the user to run .Ar command Ns s 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 .Ql cd .Ar command directly via sudo, e.g., .Bd -literal -offset 4n $ sudo cd /usr/local/protected .Ed .Pp since when the .Ar command exits the parent process (your shell) will still be the same. The .Fl D option can be used to run a .Ar command in a specific .Ar directory . .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.