tmpfs                   /dev/shm                tmpfs    defaults        0 0  
However, mount command and /proc/mounts reports only rw from defaults :
# mount -v -t tmpfs 
tmpfs on /dev/shm type tmpfs (rw)
# cat /proc/mounts | grep tmpfs
tmpfs /dev/shm tmpfs rw,seclabel,nosuid,nodev 0 0
For tmpfs, the only filesystem options that are displayed are :
size=SIZE (if the size is not default)
nr_inodes=INODES (if the number is not the default)
mode=MODE (if the mode is not the default)
uid=UID (if the uid is not 0/root)
gid=GID (if the gid is not 0/root)
memory policy (if not default)
ro/rw is displayed for all filesystem types.
Some mount options are only displayed if they are not the default.
The most complete location to view the mount options is in /proc/self/mounts in RHEL 5 and /proc/self/mountinfo in RHEL 6
      
Root Cause
For most filesystems, the mount options are only displayed in /proc/mounts if :
they are applicable to the particular filesystem type
they are not strictly for internal use
the mount options are not the default setting
the user has the appropriate capabilities to show the options (CAP_SYS_ADMIN) in the current mount namespace
      
Diagnostic Steps
        
[1] On a test system, edit fstab to mount tmpfs with rw only and performed a reboot :
# cat /etc/fstab | grep tmpfs
tmpfs                   /dev/shm                tmpfs   rw              0 0
# cd /dev/shm/
# cat > script.sh
#!/bin/bash
echo "Script ran"
# chmod u+x script.sh 
# ./script.sh 
Script ran
Result : Script ran, though exec not set.
[2] Now, edit fstab to mount tmpfs with rw,noexec and performed a reboot :
# cat /etc/fstab | grep tmpfs
tmpfs                   /dev/shm                tmpfs   rw,noexec              0 0
# cd /dev/shm/
# cat > script.sh
#!/bin/bash
echo "Script ran"
# ls -l
total 4
-rw-r--r--. 1 root root 30 Apr  6 00:47 scripts.sh
# chmod u+x script.sh
chmod: cannot access `script.sh': No such file or directory
Result : Unable to set execute permission, as noexec is set explicitly.
For example, mounting a filesystem with rw,exec options, will also mount the filesystem with suid,dev,auto, nouser,async,relatime.
But, if any of these option is unset explicitly, it will not be applicable.
                      
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