カーネル:root/include/uapi/linux/stat.h
先頭0は3ビットの8進数010 = 8

#define S_IFMT  00170000 => 15=0b1111:S_IFSOCK[1100]~S_IFIFO[0001]のファイル名称に係るビット領域

#define S_IFSOCK 0140000
#define S_IFLNK  0120000
#define S_IFREG  0100000
#define S_IFBLK  0060000
#define S_IFDIR  0040000
#define S_IFCHR  0020000
#define S_IFIFO  0010000

#define S_ISUID  0004000
#define S_ISGID  0002000
#define S_ISVTX  0001000

#define S_IRWXU    00700
#define S_IRUSR    00400
#define S_IWUSR    00200
#define S_IXUSR    00100

#define S_IRWXG    00070
#define S_IRGRP    00040
#define S_IWGRP    00020
#define S_IXGRP    00010

#define S_IRWXO    00007
#define S_IROTH    00004
#define S_IWOTH    00002
#define S_IXOTH    00001

1バイト 8ビット
typedef unsigned short[システムに関わりなく2バイト] umode_t;
umode_t inode->i_mode [1バイト8ビット:2×8=16ビット]

4ビット->ファイル名称 :S_IFSOCK/S_IFLNK/S_IFREG/S_IFBLK/S_IFDIR/S_IFCHR/S_IFIFO
3ビット->Stick :S_ISUID/S_ISGID/S_ISVTX
3ビット->User :S_IRUSR/S_IWUSR/S_IXUSR
3ビット->Group :S_IRGRP/S_IWGRP/S_IXGRP
3ビット->Other :S_IROTH/S_IWOTH/S_IXOTH

#define S_ISLNK(m)      (((m) & S_IFMT) == S_IFLNK)
#define S_ISREG(m)      (((m) & S_IFMT) == S_IFREG)
#define S_ISDIR(m)      (((m) & S_IFMT) == S_IFDIR)
#define S_ISCHR(m)      (((m) & S_IFMT) == S_IFCHR)
#define S_ISBLK(m)      (((m) & S_IFMT) == S_IFBLK)
#define S_ISFIFO(m)     (((m) & S_IFMT) == S_IFIFO)
#define S_ISSOCK(m)     (((m) & S_IFMT) == S_IFSOCK)

捕捉

[root@north dir]# cat octal.c
#include	<stdio.h>

void	main(void)
{
	printf("10進数  11=%2d\n",  11);
	printf(" 8進数 011=%2d\n", 011); 
}

[root@north dir]# ./octal.out 
10進数  11=11
 8進数 011= 9

備考

user/grop/otherのrwx属性に係る属性でないのに、lsコマンドのスティッキービットは、大文字小文字によるuser/grop/otherの実行属性に係る実装で、xs属性はS x属性はx s属性はs

係る確認は通常業務で頻繁に設定することはない故、s/S属性の違いに戸惑ってしまって、こんな実装でなく、スティッキービット表示領域としするsssとの表示すべきえはと。

[root@A0-F3-C1-17-02-A8 dir]# chmod ug-x cmd.out 
[root@A0-F3-C1-17-02-A8 dir]# ls -l cmd.out 
-rw----r-x 1 root root 7560  3月  9 14:36 cmd.out

[root@A0-F3-C1-17-02-A8 dir]# chmod ug+s cmd.out 
[root@A0-F3-C1-17-02-A8 dir]# ls -l cmd.out 
-rwS--Sr-x 1 root root 7560  3月  9 14:36 cmd.out   <xでないsはS

[root@A0-F3-C1-17-02-A8 dir]# chmod ug+x cmd.out 
[root@A0-F3-C1-17-02-A8 dir]# ls -l cmd.out 
-rws--sr-x 1 root root 7560  3月  9 14:36 cmd.out   <xでのsはs

struct inode {
       umode_t                 i_mode;
       unsigned short          i_opflags;
       kuid_t                  i_uid;
       kgid_t                  i_gid;
       unsigned int            i_flags;

#ifdef CONFIG_FS_POSIX_ACL
       struct posix_acl        *i_acl;
       struct posix_acl        *i_default_acl;
#endif

       const struct inode_operations   *i_op;
       struct super_block      *i_sb;
       struct address_space    *i_mapping;

#ifdef CONFIG_SECURITY
       void                    *i_security;
#endif

       unsigned long           i_ino;

       union {
               const unsigned int i_nlink;
               unsigned int __i_nlink;
       };
       dev_t                   i_rdev;
       loff_t                  i_size;
       struct timespec         i_atime;
       struct timespec         i_mtime;
       struct timespec         i_ctime;
       spinlock_t              i_lock; /* i_blocks, i_bytes, maybe i_size */
       unsigned short          i_bytes;
       unsigned int            i_blkbits;
       blkcnt_t                i_blocks;

#ifdef __NEED_I_SIZE_ORDERED
       seqcount_t              i_size_seqcount;
#endif
 
       unsigned long           i_state;
       struct mutex            i_mutex;

       unsigned long           dirtied_when;   /* jiffies of first dirtying */

       struct hlist_node       i_hash;
       struct list_head        i_wb_list;      /* backing dev IO list */
       struct list_head        i_lru;          /* inode LRU list */
       struct list_head        i_sb_list;
       union {
               struct hlist_head       i_dentry;
               struct rcu_head         i_rcu;
       };
       u64                     i_version;
       atomic_t                i_count;
       atomic_t                i_dio_count;
       atomic_t                i_writecount;
       const struct file_operations    *i_fop; /* former ->i_op->default_file_ops */
       struct file_lock        *i_flock;
       struct address_space    i_data;
#ifdef CONFIG_QUOTA
       struct dquot            *i_dquot[MAXQUOTAS];
#endif
       struct list_head        i_devices;
       union {
               struct pipe_inode_info  *i_pipe;
               struct block_device     *i_bdev;
               struct cdev             *i_cdev;
       };

       __u32                   i_generation;

#ifdef CONFIG_FSNOTIFY
       __u32                   i_fsnotify_mask; /* all events this inode cares about */
       struct hlist_head       i_fsnotify_marks;
#endif

#ifdef CONFIG_IMA
       atomic_t                i_readcount; /* struct files open RO */
#endif
       void                    *i_private; /* fs or device private pointer */
};