capabilities

CAPABILITIES(7)            Linux Programmer's Manual           CAPABILITIES(7)



NAME
       capabilities - overview of Linux capabilities

DESCRIPTION
       For the purpose of performing permission checks, traditional UNIX
       implementations distinguish two categories of processes: privileged
       processes (whose effective user ID is 0, referred to as superuser or
       root), and unprivileged processes (whose effective UID is nonzero).
       Privileged processes bypass all kernel permission checks, while
       unprivileged processes are subject to full permission checking based on
       the process's credentials (usually: effective UID, effective GID, and
       supplementary group list).

       Starting with kernel 2.2, Linux divides the privileges traditionally
       associated with superuser into distinct units, known as capabilities,
       which can be independently enabled and disabled.  Capabilities are a
       per-thread attribute.

   Capabilities list
       The following list shows the capabilities implemented on Linux, and the
       operations or behaviors that each capability permits:

       CAP_AUDIT_CONTROL (since Linux 2.6.11)
              Enable and disable kernel auditing; change auditing filter
              rules; retrieve auditing status and filtering rules.

       CAP_AUDIT_WRITE (since Linux 2.6.11)
              Write records to kernel auditing log.

       CAP_BLOCK_SUSPEND (since Linux 3.5)
              Employ features that can block system suspend (epoll(7)
              EPOLLWAKEUP, /proc/sys/wake_lock).

       CAP_CHOWN
              Make arbitrary changes to file UIDs and GIDs (see chown(2)).

       CAP_DAC_OVERRIDE
              Bypass file read, write, and execute permission checks.  (DAC is
              an abbreviation of "discretionary access control".)

       CAP_DAC_READ_SEARCH
              * Bypass file read permission checks and directory read and
                execute permission checks;
              * Invoke open_by_handle_at(2).


       CAP_FOWNER
              * Bypass permission checks on operations that normally require
                the file system UID of the process to match the UID of the
                file (e.g., chmod(2), utime(2)), excluding those operations
                covered by CAP_DAC_OVERRIDE and CAP_DAC_READ_SEARCH;
              * set extended file attributes (see chattr(1)) on arbitrary
                files;
              * set Access Control Lists (ACLs) on arbitrary files;
              * ignore directory sticky bit on file deletion;
              * specify O_NOATIME for arbitrary files in open(2) and fcntl(2).

       CAP_FSETID
              Don't clear set-user-ID and set-group-ID permission bits when a
              file is modified; set the set-group-ID bit for a file whose GID
              does not match the file system or any of the supplementary GIDs
              of the calling process.

       CAP_IPC_LOCK
              Lock memory (mlock(2), mlockall(2), mmap(2), shmctl(2)).

       CAP_IPC_OWNER
              Bypass permission checks for operations on System V IPC objects.

       CAP_KILL
              Bypass permission checks for sending signals (see kill(2)).
              This includes use of the ioctl(2) KDSIGACCEPT operation.

       CAP_LEASE (since Linux 2.4)
              Establish leases on arbitrary files (see fcntl(2)).

       CAP_LINUX_IMMUTABLE
              Set the FS_APPEND_FL and FS_IMMUTABLE_FL i-node flags (see
              chattr(1)).

       CAP_MAC_ADMIN (since Linux 2.6.25)
              Override Mandatory Access Control (MAC).  Implemented for the
              Smack Linux Security Module (LSM).

       CAP_MAC_OVERRIDE (since Linux 2.6.25)
              Allow MAC configuration or state changes.  Implemented for the
              Smack LSM.

       CAP_MKNOD (since Linux 2.4)
              Create special files using mknod(2).

       CAP_NET_ADMIN
              Perform various network-related operations:
              * interface configuration;
              * administration of IP firewall, masquerading, and accounting;
              * modify routing tables;
              * bind to any address for transparent proxying;
              * set type-of-service (TOS)
              * clear driver statistics;
              * set promiscuous mode;
              * enabling multicasting;
              * use setsockopt(2) to set the following socket options:
                SO_DEBUG, SO_MARK, SO_PRIORITY (for a priority outside the
                range 0 to 6), SO_RCVBUFFORCE, and SO_SNDBUFFORCE.

       CAP_NET_BIND_SERVICE
              Bind a socket to Internet domain privileged ports (port numbers
              less than 1024).

       CAP_NET_BROADCAST
              (Unused)  Make socket broadcasts, and listen to multicasts.

       CAP_NET_RAW
              * use RAW and PACKET sockets;
              * bind to any address for transparent proxying.

       CAP_SETGID
              Make arbitrary manipulations of process GIDs and supplementary
              GID list; forge GID when passing socket credentials via UNIX
              domain sockets.

       CAP_SETFCAP (since Linux 2.6.24)
              Set file capabilities.

       CAP_SETPCAP
              If file capabilities are not supported: grant or remove any
              capability in the caller's permitted capability set to or from
              any other process.  (This property of CAP_SETPCAP is not
              available when the kernel is configured to support file
              capabilities, since CAP_SETPCAP has entirely different semantics
              for such kernels.)

              If file capabilities are supported: add any capability from the
              calling thread's bounding set to its inheritable set; drop
              capabilities from the bounding set (via prctl(2)
              PR_CAPBSET_DROP); make changes to the securebits flags.

       CAP_SETUID
              Make arbitrary manipulations of process UIDs (setuid(2),
              setreuid(2), setresuid(2), setfsuid(2)); make forged UID when
              passing socket credentials via UNIX domain sockets.

       CAP_SYS_ADMIN
              * Perform a range of system administration operations including:
                quotactl(2), mount(2), umount(2), swapon(2), swapoff(2),
                sethostname(2), and setdomainname(2);
              * perform privileged syslog(2) operations (since Linux 2.6.37,
                CAP_SYSLOG should be used to permit such operations);
              * perform VM86_REQUEST_IRQ vm86(2) command;
              * perform IPC_SET and IPC_RMID operations on arbitrary System V
                IPC objects;
              * perform operations on trusted and security Extended Attributes
                (see attr(5));
              * use lookup_dcookie(2);
              * use ioprio_set(2) to assign IOPRIO_CLASS_RT and (before Linux
                2.6.25) IOPRIO_CLASS_IDLE I/O scheduling classes;
              * forge UID when passing socket credentials;
              * exceed /proc/sys/fs/file-max, the system-wide limit on the
                number of open files, in system calls that open files (e.g.,
                accept(2), execve(2), open(2), pipe(2));
              * employ CLONE_* flags that create new namespaces with clone(2)
                and unshare(2);
              * call perf_event_open(2);
              * access privileged perf event information;
              * call setns(2);
              * call fanotify_init(2);
              * perform KEYCTL_CHOWN and KEYCTL_SETPERM keyctl(2) operations;
              * perform madvise(2) MADV_HWPOISON operation;
              * employ the TIOCSTI ioctl(2) to insert characters into the
                input queue of a terminal other than the caller's controlling
                terminal.
              * employ the obsolete nfsservctl(2) system call;
              * employ the obsolete bdflush(2) system call;
              * perform various privileged block-device ioctl(2) operations;
              * perform various privileged file-system ioctl(2) operations;
              * perform administrative operations on many device drivers.

       CAP_SYS_BOOT
              Use reboot(2) and kexec_load(2).

       CAP_SYS_CHROOT
              Use chroot(2).

       CAP_SYS_MODULE
              Load and unload kernel modules (see init_module(2) and
              delete_module(2)); in kernels before 2.6.25: drop capabilities
              from the system-wide capability bounding set.

       CAP_SYS_NICE
              * Raise process nice value (nice(2), setpriority(2)) and change
                the nice value for arbitrary processes;
              * set real-time scheduling policies for calling process, and set
                scheduling policies and priorities for arbitrary processes
                (sched_setscheduler(2), sched_setparam(2));
              * set CPU affinity for arbitrary processes
                (sched_setaffinity(2));
              * set I/O scheduling class and priority for arbitrary processes
                (ioprio_set(2));
              * apply migrate_pages(2) to arbitrary processes and allow
                processes to be migrated to arbitrary nodes;
              * apply move_pages(2) to arbitrary processes;
              * use the MPOL_MF_MOVE_ALL flag with mbind(2) and move_pages(2).

       CAP_SYS_PACCT
              Use acct(2).

       CAP_SYS_PTRACE
              Trace arbitrary processes using ptrace(2); apply
              get_robust_list(2) to arbitrary processes; inspect processes
              using kcmp(2).

       CAP_SYS_RAWIO
              * Perform I/O port operations (iopl(2) and ioperm(2));
              * access /proc/kcore;
              * employ the FIBMAP ioctl(2) operation;
              * open devices for accessing x86 model-specific registers (MSRs,
                see msr(4))
              * update /proc/sys/vm/mmap_min_addr;
              * create memory mappings at addresses below the value specified
                by /proc/sys/vm/mmap_min_addr;
              * map files in /proc/bus/pci;
              * open /dev/mem and /dev/kmem;
              * perform various SCSI device commands;
              * perform certain operations on hpsa(4) and cciss(4) devices;
              * perform a range of device-specific operations on other
                devices.

       CAP_SYS_RESOURCE
              * Use reserved space on ext2 file systems;
              * make ioctl(2) calls controlling ext3 journaling;
              * override disk quota limits;
              * increase resource limits (see setrlimit(2));
              * override RLIMIT_NPROC resource limit;
              * override maximum number of consoles on console allocation;
              * override maximum number of keymaps;
              * allow more than 64hz interrupts from the real-time clock;
              * raise msg_qbytes limit for a System V message queue above the
                limit in /proc/sys/kernel/msgmnb (see msgop(2) and msgctl(2));
              * override the /proc/sys/fs/pipe-size-max limit when setting the
                capacity of a pipe using the F_SETPIPE_SZ fcntl(2) command.
              * use F_SETPIPE_SZ to increase the capacity of a pipe above the
                limit specified by /proc/sys/fs/pipe-max-size;
              * override /proc/sys/fs/mqueue/queues_max limit when creating
                POSIX message queues (see mq_overview(7));
              * employ prctl(2) PR_SET_MM operation;
              * set /proc/PID/oom_score_adj to a value lower than the value
                last set by a process with CAP_SYS_RESOURCE.

       CAP_SYS_TIME
              Set system clock (settimeofday(2), stime(2), adjtimex(2)); set
              real-time (hardware) clock.

       CAP_SYS_TTY_CONFIG
              Use vhangup(2); employ various privileged ioctl(2) operations on
              virtual terminals.

       CAP_SYSLOG (since Linux 2.6.37)

       *  Perform privileged syslog(2) operations.  See syslog(2) for
          information on which operations require privilege.

       *  View kernel addresses exposed via /proc and other interfaces when
          /proc/sys/kernel/kptr_restrict has the value 1.  (See the discussion
          of the kptr_restrict in proc(5).)

       CAP_WAKE_ALARM (since Linux 3.0)
          Trigger something that will wake up the system (set
          CLOCK_REALTIME_ALARM and CLOCK_BOOTTIME_ALARM timers).

   Past and current implementation
       A full implementation of capabilities requires that:

       1. For all privileged operations, the kernel must check whether the
          thread has the required capability in its effective set.

       2. The kernel must provide system calls allowing a thread's capability
          sets to be changed and retrieved.

       3. The file system must support attaching capabilities to an executable
          file, so that a process gains those capabilities when the file is
          executed.

       Before kernel 2.6.24, only the first two of these requirements are met;
       since kernel 2.6.24, all three requirements are met.

   Thread capability sets
       Each thread has three capability sets containing zero or more of the
       above capabilities:

       Permitted:
              This is a limiting superset for the effective capabilities that
              the thread may assume.  It is also a limiting superset for the
              capabilities that may be added to the inheritable set by a
              thread that does not have the CAP_SETPCAP capability in its
              effective set.

              If a thread drops a capability from its permitted set, it can
              never reacquire that capability (unless it execve(2)s either a
              set-user-ID-root program, or a program whose associated file
              capabilities grant that capability).

       Inheritable:
              This is a set of capabilities preserved across an execve(2).
              Inheritable capabilities remain inheritable when executing any
              program, and inheritable capabilities are added to the permitted
              set when executing a program that has the corresponding bits set
              in the file inheritable set.

              Because inheritable capabilities are not generally preserved
              across execve(2) when running as a non-root user, applications
              that wish to run helper programs with elevated capabilities
              should consider using ambient capabilities, described below.

       Effective:
              This is the set of capabilities used by the kernel to perform
              permission checks for the thread.

       Ambient (since Linux 4.3):
              This is a set of capabilities that are preserved across an
              execve(2) of a program that is not privileged.  The ambient
              capability set obeys the invariant that no capability can ever
              be ambient if it is not both permitted and inheritable.

              The ambient capability set can be directly modified using
              prctl(2).  Ambient capabilities are automatically lowered if
              either of the corresponding permitted or inheritable
              capabilities is lowered.

              Executing a program that changes UID or GID due to the set-user-
              ID or set-group-ID bits or executing a program that has any file
              capabilities set will clear the ambient set.  Ambient
              capabilities are added to the permitted set and assigned to the
              effective set when execve(2) is called.

       A child created via fork(2) inherits copies of its parent's capability
       sets.  See below for a discussion of the treatment of capabilities
       during execve(2).

       Using capset(2), a thread may manipulate its own capability sets (see
       below).

       Since Linux 3.2, the file /proc/sys/kernel/cap_last_cap exposes the
       numerical value of the highest capability supported by the running
       kernel; this can be used to determine the highest bit that may be set
       in a capability set.

   File capabilities
       Since kernel 2.6.24, the kernel supports associating capability sets
       with an executable file using setcap(8).  The file capability sets are
       stored in an extended attribute (see setxattr(2)) named
       security.capability.  Writing to this extended attribute requires the
       CAP_SETFCAP capability.  The file capability sets, in conjunction with
       the capability sets of the thread, determine the capabilities of a
       thread after an execve(2).

       The three file capability sets are:

       Permitted (formerly known as forced):
              These capabilities are automatically permitted to the thread,
              regardless of the thread's inheritable capabilities.

       Inheritable (formerly known as allowed):
              This set is ANDed with the thread's inheritable set to determine
              which inheritable capabilities are enabled in the permitted set
              of the thread after the execve(2).

       Effective:
              This is not a set, but rather just a single bit.  If this bit is
              set, then during an execve(2) all of the new permitted
              capabilities for the thread are also raised in the effective
              set.  If this bit is not set, then after an execve(2), none of
              the new permitted capabilities is in the new effective set.

              Enabling the file effective capability bit implies that any file
              permitted or inheritable capability that causes a thread to
              acquire the corresponding permitted capability during an
              execve(2) (see the transformation rules described below) will
              also acquire that capability in its effective set.  Therefore,
              when assigning capabilities to a file (setcap(8),
              cap_set_file(3), cap_set_fd(3)), if we specify the effective
              flag as being enabled for any capability, then the effective
              flag must also be specified as enabled for all other
              capabilities for which the corresponding permitted or
              inheritable flags is enabled.

   Transformation of capabilities during execve()
       During an execve(2), the kernel calculates the new capabilities of the
       process using the following algorithm:

           P'(ambient) = (file is privileged) ? 0 : P(ambient)

           P'(permitted) = (P(inheritable) & F(inheritable)) |
                           (F(permitted) & cap_bset) | P'(ambient)

           P'(effective) = F(effective) ? P'(permitted) : P'(ambient)

           P'(inheritable) = P(inheritable)    [i.e., unchanged]

       where:

           P         denotes the value of a thread capability set before the
                     execve(2)

           P'        denotes the value of a capability set after the execve(2)

           F         denotes a file capability set

           cap_bset  is the value of the capability bounding set (described
                     below).

       A privileged file is one that has capabilities or has the set-user-ID
       or set-group-ID bit set.

   Capabilities and execution of programs by root
       In order to provide an all-powerful root using capability sets, during
       an execve(2):

       1. If a set-user-ID-root program is being executed, or the real user ID
          of the process is 0 (root) then the file inheritable and permitted
          sets are defined to be all ones (i.e., all capabilities enabled).

       2. If a set-user-ID-root program is being executed, then the file
          effective bit is defined to be one (enabled).

       The upshot of the above rules, combined with the capabilities
       transformations described above, is that when a process execve(2)s a
       set-user-ID-root program, or when a process with an effective UID of 0
       execve(2)s a program, it gains all capabilities in its permitted and
       effective capability sets, except those masked out by the capability
       bounding set.  This provides semantics that are the same as those
       provided by traditional UNIX systems.

   Capability bounding set
       The capability bounding set is a security mechanism that can be used to
       limit the capabilities that can be gained during an execve(2).  The
       bounding set is used in the following ways:

       * During an execve(2), the capability bounding set is ANDed with the
         file permitted capability set, and the result of this operation is
         assigned to the thread's permitted capability set.  The capability
         bounding set thus places a limit on the permitted capabilities that
         may be granted by an executable file.

       * (Since Linux 2.6.25) The capability bounding set acts as a limiting
         superset for the capabilities that a thread can add to its
         inheritable set using capset(2).  This means that if a capability is
         not in the bounding set, then a thread can't add this capability to
         its inheritable set, even if it was in its permitted capabilities,
         and thereby cannot have this capability preserved in its permitted
         set when it execve(2)s a file that has the capability in its
         inheritable set.

       Note that the bounding set masks the file permitted capabilities, but
       not the inherited capabilities.  If a thread maintains a capability in
       its inherited set that is not in its bounding set, then it can still
       gain that capability in its permitted set by executing a file that has
       the capability in its inherited set.

       Depending on the kernel version, the capability bounding set is either
       a system-wide attribute, or a per-process attribute.

       Capability bounding set prior to Linux 2.6.25

       In kernels before 2.6.25, the capability bounding set is a system-wide
       attribute that affects all threads on the system.  The bounding set is
       accessible via the file /proc/sys/kernel/cap-bound.  (Confusingly, this
       bit mask parameter is expressed as a signed decimal number in
       /proc/sys/kernel/cap-bound.)

       Only the init process may set capabilities in the capability bounding
       set; other than that, the superuser (more precisely: programs with the
       CAP_SYS_MODULE capability) may only clear capabilities from this set.

       On a standard system the capability bounding set always masks out the
       CAP_SETPCAP capability.  To remove this restriction (dangerous!),
       modify the definition of CAP_INIT_EFF_SET in include/linux/capability.h
       and rebuild the kernel.

       The system-wide capability bounding set feature was added to Linux
       starting with kernel version 2.2.11.

       Capability bounding set from Linux 2.6.25 onward

       From Linux 2.6.25, the capability bounding set is a per-thread
       attribute.  (There is no longer a system-wide capability bounding set.)

       The bounding set is inherited at fork(2) from the thread's parent, and
       is preserved across an execve(2).

       A thread may remove capabilities from its capability bounding set using
       the prctl(2) PR_CAPBSET_DROP operation, provided it has the CAP_SETPCAP
       capability.  Once a capability has been dropped from the bounding set,
       it cannot be restored to that set.  A thread can determine if a
       capability is in its bounding set using the prctl(2) PR_CAPBSET_READ
       operation.

       Removing capabilities from the bounding set is supported only if file
       capabilities are compiled into the kernel.  In kernels before Linux
       2.6.33, file capabilities were an optional feature configurable via the
       CONFIG_SECURITY_FILE_CAPABILITIES option.  Since Linux 2.6.33, the
       configuration option has been removed and file capabilities are always
       part of the kernel.  When file capabilities are compiled into the
       kernel, the init process (the ancestor of all processes) begins with a
       full bounding set.  If file capabilities are not compiled into the
       kernel, then init begins with a full bounding set minus CAP_SETPCAP,
       because this capability has a different meaning when there are no file
       capabilities.

       Removing a capability from the bounding set does not remove it from the
       thread's inherited set.  However it does prevent the capability from
       being added back into the thread's inherited set in the future.

   Effect of user ID changes on capabilities
       To preserve the traditional semantics for transitions between 0 and
       nonzero user IDs, the kernel makes the following changes to a thread's
       capability sets on changes to the thread's real, effective, saved set,
       and file system user IDs (using setuid(2), setresuid(2), or similar):

       1. If one or more of the real, effective or saved set user IDs was
          previously 0, and as a result of the UID changes all of these IDs
          have a nonzero value, then all capabilities are cleared from the
          permitted and effective capability sets.

       2. If the effective user ID is changed from 0 to nonzero, then all
          capabilities are cleared from the effective set.

       3. If the effective user ID is changed from nonzero to 0, then the
          permitted set is copied to the effective set.

       4. If the file system user ID is changed from 0 to nonzero (see
          setfsuid(2)) then the following capabilities are cleared from the
          effective set: CAP_CHOWN, CAP_DAC_OVERRIDE, CAP_DAC_READ_SEARCH,
          CAP_FOWNER, CAP_FSETID, CAP_LINUX_IMMUTABLE (since Linux 2.2.30),
          CAP_MAC_OVERRIDE, and CAP_MKNOD (since Linux 2.2.30).  If the file
          system UID is changed from nonzero to 0, then any of these
          capabilities that are enabled in the permitted set are enabled in
          the effective set.

       If a thread that has a 0 value for one or more of its user IDs wants to
       prevent its permitted capability set being cleared when it resets all
       of its user IDs to nonzero values, it can do so using the prctl(2)
       PR_SET_KEEPCAPS operation.

   Programmatically adjusting capability sets
       A thread can retrieve and change its capability sets using the
       capget(2) and capset(2) system calls.  However, the use of
       cap_get_proc(3) and cap_set_proc(3), both provided in the libcap
       package, is preferred for this purpose.  The following rules govern
       changes to the thread capability sets:

       1. If the caller does not have the CAP_SETPCAP capability, the new
          inheritable set must be a subset of the combination of the existing
          inheritable and permitted sets.

       2. (Since Linux 2.6.25) The new inheritable set must be a subset of the
          combination of the existing inheritable set and the capability
          bounding set.

       3. The new permitted set must be a subset of the existing permitted set
          (i.e., it is not possible to acquire permitted capabilities that the
          thread does not currently have).

       4. The new effective set must be a subset of the new permitted set.

   The securebits flags: establishing a capabilities-only environment
       Starting with kernel 2.6.26, and with a kernel in which file
       capabilities are enabled, Linux implements a set of per-thread
       securebits flags that can be used to disable special handling of
       capabilities for UID 0 (root).  These flags are as follows:

       SECBIT_KEEP_CAPS
              Setting this flag allows a thread that has one or more 0 UIDs to
              retain its capabilities when it switches all of its UIDs to a
              nonzero value.  If this flag is not set, then such a UID switch
              causes the thread to lose all capabilities.  This flag is always
              cleared on an execve(2).  (This flag provides the same
              functionality as the older prctl(2) PR_SET_KEEPCAPS operation.)

       SECBIT_NO_SETUID_FIXUP
              Setting this flag stops the kernel from adjusting capability
              sets when the threads's effective and file system UIDs are
              switched between zero and nonzero values.  (See the subsection
              Effect of User ID Changes on Capabilities.)

       SECBIT_NOROOT
              If this bit is set, then the kernel does not grant capabilities
              when a set-user-ID-root program is executed, or when a process
              with an effective or real UID of 0 calls execve(2).  (See the
              subsection Capabilities and execution of programs by root.)

       SECBIT_NO_CAP_AMBIENT_RAISE
              Setting this flag disallows raising ambient capabilities via the
              prctl(2) PR_CAP_AMBIENT_RAISE operation.

       Each of the above "base" flags has a companion "locked" flag.  Setting
       any of the "locked" flags is irreversible, and has the effect of
       preventing further changes to the corresponding "base" flag.  The
       locked flags are: SECBIT_KEEP_CAPS_LOCKED,
       SECBIT_NO_SETUID_FIXUP_LOCKED, SECBIT_NOROOT_LOCKED, and
       SECBIT_NO_CAP_AMBIENT_RAISE.

       The securebits flags can be modified and retrieved using the prctl(2)
       PR_SET_SECUREBITS and PR_GET_SECUREBITS operations.  The CAP_SETPCAP
       capability is required to modify the flags.

       The securebits flags are inherited by child processes.  During an
       execve(2), all of the flags are preserved, except SECBIT_KEEP_CAPS
       which is always cleared.

       An application can use the following call to lock itself, and all of
       its descendants, into an environment where the only way of gaining
       capabilities is by executing a program with associated file
       capabilities:

           prctl(PR_SET_SECUREBITS,
                   SECBIT_KEEP_CAPS_LOCKED |
                   SECBIT_NO_SETUID_FIXUP |
                   SECBIT_NO_SETUID_FIXUP_LOCKED |
                   SECBIT_NOROOT |
                   SECBIT_NOROOT_LOCKED);

CONFORMING TO
       No standards govern capabilities, but the Linux capability
       implementation is based on the withdrawn POSIX.1e draft standard; see
       ⟨http://wt.tuxomania.net/publications/posix.1e/⟩.

NOTES
       Since kernel 2.5.27, capabilities are an optional kernel component, and
       can be enabled/disabled via the CONFIG_SECURITY_CAPABILITIES kernel
       configuration option.

       The /proc/PID/task/TID/status file can be used to view the capability
       sets of a thread.  The /proc/PID/status file shows the capability sets
       of a process's main thread.  Before Linux 3.8, nonexistent capabilities
       were shown as being enabled (1) in these sets.  Since Linux 3.8, all
       non-existent capabilities (above CAP_LAST_CAP) are shown as disabled
       (0).

       The libcap package provides a suite of routines for setting and getting
       capabilities that is more comfortable and less likely to change than
       the interface provided by capset(2) and capget(2).  This package also
       provides the setcap(8) and getcap(8) programs.  It can be found at
       ⟨http://www.kernel.org/pub/linux/libs/security/linux-privs⟩.

       Before kernel 2.6.24, and since kernel 2.6.24 if file capabilities are
       not enabled, a thread with the CAP_SETPCAP capability can manipulate
       the capabilities of threads other than itself.  However, this is only
       theoretically possible, since no thread ever has CAP_SETPCAP in either
       of these cases:

       * In the pre-2.6.25 implementation the system-wide capability bounding
         set, /proc/sys/kernel/cap-bound, always masks out this capability,
         and this can not be changed without modifying the kernel source and
         rebuilding.

       * If file capabilities are disabled in the current implementation, then
         init starts out with this capability removed from its per-process
         bounding set, and that bounding set is inherited by all other
         processes created on the system.

SEE ALSO
       capget(2), prctl(2), setfsuid(2), cap_clear(3), cap_copy_ext(3),
       cap_from_text(3), cap_get_file(3), cap_get_proc(3), cap_init(3),
       capgetp(3), capsetp(3), libcap(3), credentials(7), pthreads(7),
       getcap(8), setcap(8)

       include/linux/capability.h in the Linux kernel source tree

COLOPHON
       This page is part of release 3.53 of the Linux man-pages project.  A
       description of the project, and information about reporting bugs, can
       be found at http://www.kernel.org/doc/man-pages/.



Linux                             2013-07-21                   CAPABILITIES(7)