OneAgent non-privileged mode on Linux

  • 7-min read
  • Published Jul 19, 2017

By default, OneAgent is installed in the non-privileged mode, in which superuser privileges are used once to initiate the installation process.

OneAgent is then run under an unprivileged user, retaining the complete set of functionalities.

System requirements

To install OneAgent in non-privileged mode, your system must meet the following requirements:

  • The filesystem must support extended attributes.
  • The system must have libcap2 installed. For example, the default Red Hat Enterprise Linux 5 installation doesn't have libcap2.
  • The filesystem must not be mounted as noexec or nosuid.
  • Linux Filesystem Capabilities must be enabled. For example, SUSE Linux Enterprise Server 11 has Linux Filesystem Capabilities disabled by default. For more information, see Non-privileged mode and Linux Filesystem Capabilities below.

See OneAgent security on Linux to learn about monitoring actions executed by OneAgent that require privileged access.

Privileges during installation

When run in non-privileged mode, the OneAgent installer requires superuser privileges to:

  • Set file capabilities for OneAgent binaries located at /opt/dynatrace/oneagent/agent/lib[64]/*.
  • Invoke the oneagent service script to start oneagentwatchdog.
  • On systems with systemd, communicate with systemd daemon via d-bus to run the following commands:
    • systemctl <start|stop|enable|disable> oneagent.service
    • systemctl daemon-reload
  • On systems with SysV, execute /sbin/chkconfig to add the oneagent service script to autostart or to remove it.
  • Write to /proc/sys/kernel/core_pattern.

Superuser privileges are dropped when the Dynatrace OneAgent service script is executed:

  • On systems with systemd, the unprivileged user is included in the service definition (unit file). The systemd daemon thus runs the OneAgent service script in unprivileged mode.
  • On systems with SysV, the privileges are dropped in the script when starting the OneAgent Watchdog process.

Linux System Capabilities

Dynatrace OneAgent Watchdog starts and runs all other processes under an unprivileged user without superuser access. OneAgent binaries leverage the following Linux System Capabilities.

Binary
Linux System Capabilities
oneagentwatchdog
cap_sys_resource1- for setting system resource limits when starting OneAgent processes
oneagentos
cap_dac_override2 - for filesystem access
cap_chown2 3 - for setting ownership of files replaced in the filesystem (e.g., runc binary)
cap_fowner 2 - for setting ownership of files replaced in the filesystem
cap_sys_ptrace - for reading data from /proc pseudo-filesystem and tracing processes
cap_sys_resource3 - for reading processes resource limits
cap_setuid4 - for temporary elevation of privileges to execute certain operations; for details, see Automatic updates and operation
cap_kill 3 5 6
cap_setfcap 3 5 6
cap_fsetid 3 5 6
oneagentnettracer
cap_bpf (kernel >=5.8)7
cap_perfmon (kernel >=5.8)7
cap_sys_admin (kernel <5.8, or when cap_bpf is explicitly blocked)7
cap_dac_override
cap_sys_ptrace
cap_sys_resource
oneagentnetwork
cap_net_raw - for opening raw sockets
cap_net_admin8- for reading network interface information
oneagentloganalytics
cap_dac_read_search - for access to all logs stored on host
cap_sys_ptrace - for reading data from /proc pseudo-filesystem
oneagentplugin
cap_set_gid1- for adding docker to the process supplementary groups list, which allows for the container data to be retrieved
oneagenthelper9
cap_sys_admin - for mount() syscall
cap_dac_override - for inspection and modification of filesystems of the running containers
cap_sys_ptrace - for tracing the Docker daemon
cap_sys_chroot - for chroot() syscall
cap_fowner - for changing ownership and permissions of files within container filesystem
cap_fsetid - for changing ownership and permissions of files within container filesystem
OneAgent Installer executed during auto-update
cap_dac_override - for filesystem access
cap_chown - for filesystem access
cap_fowner - for filesystem access
cap_fsetid - for filesystem access
cap_kill - to be able to signal all the running processes, e.g. stopped orphaned OneAgent processes
cap_setfcap - for setting Linux Filesystem capabilities file capabilities on agent binaries during the installation
oneagentosconfig
cap_setuid6- for execution of privileged operations during the installation process
cap_setgid6- for setting group ownership of files during the installation process
oneagenteventstracer
cap_sys_admin - for perf_event_open() syscall
cap_dac_override - for access to /sys/kernel/debug/tracing
oneagentdmidecode
cap_dac_override - for filesystem access
oneagentmntconstat
cap_dac_read_search - for retrieving disk occupation stats with statvfs64()
cap_sys_chroot - for setns() syscall
cap_sys_admin - for setns() syscall
cap_sys_ptrace - for accessing /proc/1/ns
oneagentebpfdiscovery
cap_bpf (kernel >=5.8)7
cap_perfmon (kernel >=5.8)7
cap_sys_admin (kernel <5.8, or when cap_bpf is explicitly blocked)7
cap_dac_override - for write access to /sys/kernel/debug/tracing
cap_sys_resource - for removing memory usage limitation of the bpf program
1

Required only during initialization phase and is unconditionally dropped afterwards.

2

Not used if auto-updates and automatic injection are disabled.

3

Kept in permitted set only and raised to the effective set when needed.

4

Only if ambient capabilities aren't supported.

5

Not used if auto-updates are disabled.

6

Only if ambient capabilities are supported.

7

Only for kernels 5.8 and newer, unless usage of unprivileged cap_bpf is blocked by the OS, then it fallbacks to cap_sys_admin. For older kernel versions, cap_sys_admin is enabled instead.

8

Only on kernels older than 2.6.33.

9

Not started if automatic injection is disabled.

Linux Filesystem Capabilities are required to install OneAgent in non-privileged mode. SUSE Linux Enterprise Server 11 has Linux Filesystem Capabilities disabled by default. These capabilities might also be disabled in other supported Linux distributions or as the result of a custom configuration. The OneAgent installer prints the following message if Linux Filesystem Capabilities are disabled:

Warning: Failed to enable non-privileged mode, kernel does not support file capabilities.

You can also check the kernel boot options to see if Linux Filesystem Capabilities are enabled. Run the following command to check your kernel boot options.

cat /proc/cmdline

If you find file_caps=1 in the output, your setup is fine.

To enable Linux Filesystem Capabilities, add file_caps=1 to your kernel boot options. For example, on SUSE Linux Enterprise Server 11, use YaST, edit kernel boot options, add file_caps=1, and reboot the machine.

Privileges during automatic updates and operation

The scope of privileges required by OneAgent depends on whether the kernel supports Linux ambient capabilities. As a general rule, kernel 4.3+ supports ambient capabilities. However, in the case of Red Hat Enterprise Linux, these may be supported in older kernel versions because of the Red Hat policy to backport patches. This makes ambient capabilities supported by kernel versions as old as 3.10.x.

During an automatic update, the installer starts under an unprivileged dtuser with proper ambient capabilities set. OneAgent doesn't require root access to perform an automatic update.

Red Hat Enterprise Linux 7 has a too low systemd (v219 instead of the required v221), and to be able to run automatic updates in non-privileged mode, we're temporarily elevating the privileges to run systemctl <start|stop|enable|disable> oneagent.service.

How do I know if OneAgent operates in non-privileged mode?

The installer prints a message at the end of OneAgent installation. Depending on the kernel version and its support for ambient capabilities, you will see one of the following messages:

  • Non-privileged mode is enabled
    The kernel supports ambient capabilities, the root access is not used for updates or operation.
  • Enabled non-privileged mode, but ambient capabilities are not supported by kernel
    The kernel is within the minimum supported version, but due to non-supported ambient capabilities, OneAgent needs to elevate privileges in select cases, see above.
  • Failed to enable non-privileged mode
    The kernel doesn't meet the minimum version requirements to enable non-privileged mode.