Linux xfs文件系统stat命令Birth字段为空的原因探究
2023-05-10 22:31 潇湘隐者 阅读(451) 评论(0) 编辑 收藏 举报在Linux平台找出某个目录下创建时间最早的文件,测试验证脚本结果是否准确的过程中发现一个很有意思的现象,stat命令在一些平台下Birth字段有值,而在一些平台则为空值,如下所示:
RHEL 8.7下, XFS文件系统
[mysql@mysqlu02 ~]$ more /etc/redhat-release
Red Hat Enterprise Linux release 8.7 (Ootpa)
[mysql@mysqlu02 ~]$ touch test.txt
[mysql@mysqlu02 ~]$ stat test.txt
File: test.txt
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: fd05h/64773d Inode: 144 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 801/ mysql) Gid: ( 800/ mysql)
Access: 2023-05-06 17:09:44.428050549 +0800
Modify: 2023-05-06 17:09:44.428050549 +0800
Change: 2023-05-06 17:09:44.428050549 +0800
Birth: 2023-05-06 17:09:44.428050549 +0800
![](https://files.mdnice.com/user/234/85c66572-d4b4-48a2-ba68-14b6d001b2df.png)
RHEL 7.9 XFS文件系统
[oracle@KerryDB ~]$ more /etc/redhat-release
Red Hat Enterprise Linux Server release 7.9 (Maipo)
[oracle@KerryDB ~]$ touch test.txt
[oracle@KerryDB ~]$ stat test.txt
File: ‘test.txt’
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: fd03h/64771d Inode: 4238838 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 700/ oracle) Gid: ( 600/oinstall)
Access: 2023-05-06 17:03:42.964517675 +0800
Modify: 2023-05-06 17:03:42.964517675 +0800
Change: 2023-05-06 17:03:42.964517675 +0800
Birth: -
[oracle@KerryDB ~]$
![](https://files.mdnice.com/user/234/59dd5e71-edd5-43d4-8cd8-9ca284fb9018.png)
stat命令的Birth字段表示文件的创建时间,该属性是ext4的新功能(当然也适用于xfs文件系统),也称为crtime或btime,但是当前两个测试环境的文件系统为xfs,之前也在xfs文件系统中测试过,发现xfs不支持creation time. 但是从xfs v5开始,xfs已经支持creation time,文档[1]中已有阐述,如下所示:
/* version 5 filesystem (inode version 3) fields start here */
__le32 di_crc;
__be64 di_changecount;
__be64 di_lsn;
__be64 di_flags2;
__be32 di_cowextsize;
__u8 di_pad2[12];
xfs_timestamp_t di_crtime;
__be64 di_ino;
uuid_t di_uuid;
};
*di_crtime*::
Specifies the time when this inode was created.
但是上面这个差异现象,还是让我有点好奇,因为两个测试环境对应的xfs版本都是v5,如下所示。
KerryDB这台机器的xfs版本信息:
Oracle用户:
$ uname -r
3.10.0-1160.80.1.el7.x86_64
$ dmesg | grep -iE 'xfs.*\s+mounting' | head -1
[ 4.041026] XFS (dm-0): Mounting V5 Filesystem
root用户:
# xfs_db -r /dev/mapper/vg00-home
xfs_db> version
versionnum [0xb4b5+0x18a] = V5,NLINK,DIRV2,ATTR,ALIGN,LOGV2,EXTFLG,MOREBITS,ATTR2,LAZYSBCOUNT,PROJID32BIT,CRC,FTYPE
xfs_db>
mysqlu02这台机器的xfs版本信息:
mysql用户:
$ dmesg | grep -iE 'xfs.*\s+mounting' | head -1
[ 7.654324] XFS (dm-0): Mounting V5 Filesystem
root用户:
# xfs_db -r /dev/mapper/vg00-home
xfs_db> version
versionnum [0xb4b5+0x18a] = V5,NLINK,DIRV2,ATTR,ALIGN,LOGV2,EXTFLG,MOREBITS,ATTR2,LAZYSBCOUNT,PROJID32BIT,CRC,FTYPE,FINOBT,SPARSE_INODES,REFLINK
xfs_db>
那么到底是什么原因导致。Google搜索了相关资料,原来,如果stat命令查看xfs文件系统的文件时,如果要Birth字段不显示空置,必须满足几个条件,一个是xfs的版本为v5,另外,对操作系统内核版本也有要求(如下所示)
stat “now prints file creation time when supported by the file system, on GNU Linux systems with glibc >= 2.28 and kernel >= 4.11.”
KerryDB这台服务器内核信息如下所示
$ uname -r
3.10.0-1160.80.1.el7.x86_64
mysqlu02这台服务器的内核信息如下所示:
$ uname -r
4.18.0-425.3.1.el8.x86_64
如上所示,stat命令Birth字段为空置的操作系统内核版本为3.10.0,不满足条件kernerl >=4.11 所以stat命令显示空值。
参考资料
1: https://git.kernel.org/pub/scm/fs/xfs/xfs-documentation.git/tree/design/XFS_Filesystem_Structure/ondisk_inode.asciidoc
![](https://images.cnblogs.com/cnblogs_com/kerrycode/1913302/o_240731062102_kerrycode.png)