df 显示文件系统满了但还有2G空间未用

问题：df 显示文件系统满了但还有2G空间未用

sles11sp1-x64:/opt # ls
coreutils-6.12-32.39.1.x86_64.rpm  coreutils-lang-6.12-32.39.1.x86_64.rpm  kde3  vmware_time

sles11sp1-x64:/opt # rpm -Uvh coreutils-*  
Preparing...                ########################################### [100%]
   1:coreutils-lang         ########################################### [ 50%]
   2:coreutils              ########################################### [100%]
sles11sp1-x64:/opt # df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              29G   27G     0 100% /
devtmpfs              1.5G  112K  1.5G   1% /dev
tmpfs                 1.5G     0  1.5G   0% /dev/shm

sles11sp1-x64:/opt # mount
/dev/sda2 on / type ext3 (rw,acl,user_xattr)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
debugfs on /sys/kernel/debug type debugfs (rw)
devtmpfs on /dev type devtmpfs (rw,mode=0755)
tmpfs on /dev/shm type tmpfs (rw,mode=1777)
devpts on /dev/pts type devpts (rw,mode=0620,gid=5)
fusectl on /sys/fs/fuse/connections type fusectl (rw)
securityfs on /sys/kernel/security type securityfs (rw)


sles11sp1-x64:/opt # df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda2             29451020  28102340         0 100% /
devtmpfs               1512400       112   1512288   1% /dev
tmpfs                  1512400         0   1512400   0% /dev/shm

sles11sp1-x64:/opt # df -i
Filesystem            Inodes   IUsed   IFree IUse% Mounted on
/dev/sda2            1872304  411579 1460725   22% /
devtmpfs                   0       0       0    -  /dev
tmpfs                 378100       1  378099    1% /dev/shm


根因分析：

strace  df  /dev/sda2  发现结果是 statfs的结果，其中

statfs("/", {f_type="EXT2_SUPER_MAGIC", f_bsize=4096, f_blocks=7362755, f_bfree=335618, f_bavail=0, f_files=1872304, f_ffree=1460461, f_fsid={-412611788, 800243945}, f_namelen=255, f_frsize=4096}) = 0



sles11sp1-x64:/opt # strace -o df.txt df  /dev/sda2
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda2             29451020  28103356         0 100% /


statfs("/", {f_type="EXT2_SUPER_MAGIC", f_bsize=4096, f_blocks=7362755, f_bfree=336916, f_bavail=0, f_files=1872304, f_ffree=1460725, f_fsid={-412611788, 800243945}, f_namelen=255, f_frsize=4096}) = 0
 
 
struct fs_usage
{
  uintmax_t fsu_blocksize;      /* Size of a block.  */
  uintmax_t fsu_blocks;         /* Total blocks. */
  uintmax_t fsu_bfree;          /* Free blocks available to superuser. */
  uintmax_t fsu_bavail;         /* Free blocks available to non-superuser. */
  bool fsu_bavail_top_bit_set;  /* 1 if fsu_bavail represents a value < 0.  */
  uintmax_t fsu_files;          /* Total file nodes. */
  uintmax_t fsu_ffree;          /* Free file nodes. */
};  

available 字段域显示的是 fsu_bavail ，  就是非root用户可用的空闲空间。

以普通用户身份登录上去，发现果然如此：

hujun@jun:~/Desktop> ssh hujun@192.168.101.40
Password:
Last login: Fri Mar 14 16:23:13 2014 from jun.dnsdhcp.apac.novell.com
hujun@sles11sp1-x64:~> ls
bin
hujun@sles11sp1-x64:~> df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              29G   27G     0 100% /
devtmpfs              1.5G  112K  1.5G   1% /dev
tmpfs                 1.5G  100K  1.5G   1% /dev/shm
df: `/root/.gvfs': Permission denied
hujun@sles11sp1-x64:~> touch a.txt
hujun@sles11sp1-x64:~> df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda2             29451020  28108548         0 100% /
devtmpfs               1512400       112   1512288   1% /dev
tmpfs                  1512400       100   1512300   1% /dev/shm

hujun@sles11sp1-x64:~> dd if=/dev/zero of=bigfile bs=512 count=1
dd: writing `bigfile': No space left on device
1+0 records in
0+0 records out
0 bytes (0 B) copied, 0.000199858 s, 0.0 kB/s


hujun@sles11sp1-x64:~> echo "abcd" > hello
-bash: echo: write error: No space left on device
hujun@sles11sp1-x64:~> df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              29G   27G     0 100% /
devtmpfs              1.5G  112K  1.5G   1% /dev
tmpfs                 1.5G  100K  1.5G   1% /dev/shm
df: `/root/.gvfs': Permission denied

以root用户身份登录上去，是可以的。

hujun@sles11sp1-x64:~> su -
Password:
sles11sp1-x64:~ # df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2              29G   27G     0 100% /
devtmpfs              1.5G  112K  1.5G   1% /dev
tmpfs                 1.5G  100K  1.5G   1% /dev/shm
sles11sp1-x64:~ # dd if=/dev/zero of=bigfile bs=1M count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 378.163 s, 2.8 MB/s