自内核 2.2 版本开始，Linux 将传统上与超级用户关联的特权分为几个单元，称为 capabilities （权能），它们可以被独立的启用或禁用。权能是每个线程的属性。
下面的列表展示了 Linux 上实现的权能，以及每种权能允许的 *** 作或行为：
权能的完整实现需要：
在内核 2.6.24 之前，只有前两个要求能够满足；自内核 2.6.24 开始，所有三个要求都能满足。
每个线程具有三个包含零个或多个上面的权能的权能集合：
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 kernelthis can be used to determine the highest bit that may be set in a capability set.
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:
During an execve(2), the kernel calculates the new capabilities of the process using the following algorithm:
其中：
A privileged file is one that has capabilities or has the set-user-ID or set-group-ID bit set.
In order to provide an all-powerful root using capability sets, during an execve(2):
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.
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:
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.
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/capbound.)
Only the init process may set capabilities in the capability bounding setother 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.
From Linux 2.6.25, the capability bounding set is a per-thread attribute. (There is no longer a systemwide 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.
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 filesystem user IDs (using setuid(2), setresuid(2), or similar):
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 or the SECBIT_KEEP_CAPS securebits flag described below.
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:
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:
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:
For a discussion of the interaction of capabilities and user namespaces, see user_namespaces(7).
No standards govern capabilities, but the Linux capability implementation is based on the withdrawn POSIX.1e draft standardsee ⟨ http://wt.tuxomania.net/publications/posix.1e/ ⟩.
From kernel 2.5.27 to kernel 2.6.26, capabilities were 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 nonexistent 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 from kernel 2.6.24 to kernel 2.6.32 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:
capsh(1), setpriv(1), 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), user_namespaces(7), pthreads(7), getcap(8), setcap(8)
include/linux/capability.h in the Linux kernel source tree
This page is part of release 4.04 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at http://www.kernel.org/doc/man-pages/ .
1、查看依赖库1.1、查看可执行文件依赖的库有哪些
举例，查看常用的ls工具，依赖哪些库：
1.2、查看动态库，依赖的库有哪些
举例，查看libcap依赖的库有哪些：
1. 安装CentOS，注意先不要创建oracle用户，语言务必选择英语；2. 获取Oracle 11G安装包；
3. 创建Oracle安装目录；
1) 创建用户：oracle，组：oinstall，dba；
1) groupadd oinstall #创建用户组oinstall
2) groupadd dba #创建用户组dba
3) useradd -g oinstall -g dba -m oracle #创建用户oracle，并加入oinstall和dba用户组
4) passwd oracle #设置用户oracle的登录密码，根据提示输入两次密码
5) mkdir /oracle #创建Oracle安装目录
6) chown -R oracle:oinstall /oracle #设置目录所有者为oinstall用户组的oracle用户
1. 修改内核参数；
这一步修改主要是因为，在oracle的官方文档中有对oracle数据库安装配置的最低要求，因此需要修改一下
vi /etc/sysctl.conf #编辑，
#在最后添加以下代码
net.ipv4.icmp_echo_ignore_broadcasts = 1
net.ipv4.conf.all.rp_filter = 1
fs.file-max = 6815744
fs.aio-max-nr = 1048576
kernel.shmall = 2097152
kernel.shmmax = 2147483648
kernel.shmmni = 4096
kernel.sem = 250 32000 100 128
net.ipv4.ip_local_port_range = 9000 65500
net.core.rmem_default = 262144
net.core.rmem_max= 4194304
net.core.wmem_default= 262144
net.core.wmem_max= 1048576
保存退出后要进行如下 *** 作以使配置生效
sysctl -p #使配置立即生效
2. 设置oracle用户限制
vi /etc/security/limits.conf #在末尾添加以下代码
oracle soft nproc 2047
oracle hard nproc 16384
oracle soft nofile 1024
oracle hard nofile 65536
3. 关闭SELINUX
vi /etc/selinux/config
#编辑配置文件
#注释掉SELINUX=enforcing
# 注释掉SELINUXTYPE=targeted
SELINUX=disabled #增加
4. 安装必备软件；
yum install gcc* gcc-* gcc-c++-* glibc-devel-* glibc-headers-* compat-libstdc* libstdc* elfutils-libelf-devel* libaio-devel* sysstat* unixODBC-* pdksh-*
5. 检查依赖关系
binutils-2.23.52.0.1-12.el7.x86_64
compat-libcap1-1.10-3.el7.x86_64
gcc-4.8.2-3.el7.x86_64
gcc-c++-4.8.2-3.el7.x86_64
glibc-2.17-36.el7.i686
glibc-2.17-36.el7.x86_64
glibc-devel-2.17-36.el7.i686
glibc-devel-2.17-36.el7.x86_64
ksh
libaio-0.3.109-9.el7.i686
libaio-0.3.109-9.el7.x86_64
libaio-devel-0.3.109-9.el7.i686
libaio-devel-0.3.109-9.el7.x86_64
libgcc-4.8.2-3.el7.i686
libgcc-4.8.2-3.el7.x86_64
libstdc++-4.8.2-3.el7.i686
libstdc++-4.8.2-3.el7.x86_64
libstdc++-devel-4.8.2-3.el7.i686
libstdc++-devel-4.8.2-3.el7.x86_64
libXi-1.7.2-1.el7.i686
libXi-1.7.2-1.el7.x86_64
libXtst-1.2.2-1.el7.i686
libXtst-1.2.2-1.el7.x86_64
make-3.82-19.el7.x86_64
sysstat-10.1.5-1.el7.x86_64
6. 配置用户的环境变量（可以安装完再设置）
vi /home/oracle/.bash_profile
#在最后添加以下代码
export ORACLE_BASE=/oracle/app/oracle #oracle数据库安装目录
export ORACLE_HOME=$ORACLE_BASE/product/11.2.0/dbhome_1 #oracle数据库路径
export ORACLE_SID=orcl #oracle启动数据库实例名
export ORACLE_TERM=xterm #xterm窗口模式安装
export PATH=$ORACLE_HOME/bin:/usr/sbin:$PATH #添加系统环境变量
export LD_LIBRARY_PATH=$ORACLE_HOME/lib:/lib:/usr/lib #添加系统环境变量
export #防止安装过程出现乱码
export NLS_LANG=AMERICAN_AMERICA.ZHS16GBK #设置Oracle客户端字符集，必须与Oracle安装时设置的字符集保持一致，如：ZHS16GBK，否则出现数据导入导出中文乱码问题
保存退出以后，输入如下命令使配置生效
source .bash_profile #使设置立刻生效
7. 运行如下命令启动安装界面
export LANG=en_US #设置编码，防止图形界面乱码
./runInstaller [jarLoc=]
8. “ins_ctx.mk”错误处理
下载下面的文件，解压后使用其中libstdc++替换/usr/lib64目录下的同名文件即可
9. “ins_emagent.mk”编译错误，未解决，但未发现影响使用。
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